Design System Inspiration of Mercari

1. Visual Theme & Atmosphere

Mercari is Japan's largest C2C marketplace (50M+ downloads, 350K daily listings) and its design system is a textbook example of mature semantic token architecture. The production site at jp.mercari.com exposes 681 CSS custom properties on :root, organized into the well-named --alias-color-* namespace: --alias-color-background-{role}-{state}, --alias-color-text-{role}-{state}, --alias-color-border-{role}-{state}, --alias-color-icon-{role}-{state}, --alias-color-overlay-*. This isn't internal documentation — it's the actual design system surfaced at runtime, ready to read directly from any production page.

The brand color is the famous Mercari Red (#ff333f) — vivid, attention-grabbing, used as the attention semantic role for badges, error states, danger actions, and the iconic price-tag aesthetic. Around it sits a balanced palette: accent blue (#0095ee), success green (#0aa466), decorative yellow (#ffb818). Text hierarchy uses dark gray (#333333 primary, #666666 secondary) on a pure white surface (#ffffff), with a soft secondary background (#f5f5f5) for grouped sections.

Typography is system-stack with Japanese-first fallbacks: Helvetica Neue, Arial, Hiragino Kaku Gothic ProN Custom, Hiragino Sans Custom, Meiryo Custom, sans-serif. The "Custom" suffix on the Hiragino/Meiryo fonts indicates Mercari's deployment of optically-tuned variants for their production app — same font families, but adjusted spacing/hinting for marketplace UI. Buttons use weight 700 for primary CTAs at a tight 4px radius, while body text holds at weight 400.

Key Characteristics:

• 681 semantic CSS custom properties exposed on :root — the public design system surface
• Mercari Red (#ff333f) as the attention semantic — used for badges, error/danger states, sale prices, the brand mark
• Japanese-first font stack: Helvetica Neue → Arial → Hiragino Kaku Gothic ProN Custom → Hiragino Sans Custom → Meiryo Custom
• Fixed 4px border-radius on buttons and cards — sharp, commerce-functional
• Weight 700 for primary CTAs; weight 400 for body and secondary controls
• Three-tier color naming: alias-color-{property}-{role}-{state} (e.g., --alias-color-background-attention-default)
• 1440px max page width with --grid-layout-gutter: 24px and --grid-layout-page-padding-horizontal: 36px
• 4dp spacing micro-scale (--bnfXaU: 6px, --exLgvR: 8px, --fwPfWM: 8px, etc.) with named alias tokens
• High-density product grid with circular brand thumbnails (border-radius: 50%) for category navigation
• Multi-tier z-index system: dialog 1400, modal 1400, snackbar 1500, tooltip 1600

2. Color Palette & Roles

All values verified live from :root CSS custom properties on jp.mercari.com.

Brand / Attention (the Mercari Red family)

• Mercari Red (#ff333f): --alias-color-background-attention-default, --alias-color-text-attention-default. The signature brand red. Used for danger actions, sale price emphasis, the brand mark.
• Red Highlight (#ff6574): --alias-color-background-attention-highlight, --alias-color-border-attention-highlight. Lighter variant for hover states.
• Red Active (#e32b36): --alias-color-background-attention-active, --alias-color-border-attention-active. Pressed state.
• Red Thin (#fdf1f3): --alias-color-background-attentionThin-default. Very light pink for subtle background emphasis (e.g., error message bg).
• Red Thin Highlight (#ffdcdf): --alias-color-background-attentionThin-highlight.

Accent (Mercari Blue)

• Accent Blue (#0095ee): --alias-color-background-accent-default, --alias-color-text-accent-default, --alias-color-icon-accent-default. Links, info badges, accent CTAs.
• Accent Blue Highlight (#63c5ff): --alias-color-background-accent-highlight.
• Accent Blue Active (#0073cc): --alias-color-background-accent-active, --alias-color-text-accent-active.
• Link Default (#0073cc): --alias-color-text-link-default, --alias-color-icon-link-default.
• Link Highlight (#30b2ff): --alias-color-text-link-highlight.
• Link Active (#0056ab): --alias-color-text-link-active.
• Accent Thin (#e8f8ff): --alias-color-background-accentThin-default. Light blue notification bg.

Success

• Success Green (#0aa466): --alias-color-text-success-default, --alias-color-icon-success-default, --alias-color-border-success-default.
• Success Highlight (#0fbf67): --alias-color-text-success-highlight, --alias-color-icon-success-highlight.
• Success Active (#078962): --alias-color-text-success-active, --alias-color-icon-success-active.
• Success Thin (#e4ffec): --alias-color-background-success-default.
• Success Thin Highlight (#cdfbd2): --alias-color-background-success-highlight.

Decorative (Yellow)

• Decorative Yellow (#ffb818): --alias-color-icon-decorativeYellow-default. Reviews, ratings, premium markers.
• Decorative Yellow Highlight (#ffdc74): Lighter yellow for hover.
• Decorative Yellow Active (#db9611): Darker amber for pressed.

Text (5-tier scale)

• Primary (#333333): --alias-color-text-primary-default. Default body text and headlines.
• Primary Highlight (#999999): --alias-color-text-primary-highlight.
• Primary Active (#222222): --alias-color-text-primary-active.
• Secondary (#666666): --alias-color-text-secondary-default. Captions, metadata.
• Secondary Highlight (#999999): --alias-color-text-secondary-highlight.
• Secondary Active (#4c4c4c): --alias-color-text-secondary-active.
• Disabled (#cccccc): --alias-color-text-disabled-default.
• Placeholder (#999999): --alias-color-text-placeholder-default.
• Inverse (#ffffff): --alias-color-text-inverse-default. White text on dark surfaces.

Background / Surface (5-tier scale)

• Primary (#ffffff): --alias-color-background-primary-default. Default page bg.
• Primary Active (#f5f5f5): --alias-color-background-primary-active. Pressed/hover state for white-bg controls.
• Primary Highlight (#f5f5f5): --alias-color-background-primary-highlight.
• Secondary (#f5f5f5): --alias-color-background-secondary-default. Grouped section bg.
• Secondary Highlight (#e5e5e5): --alias-color-background-secondary-highlight.
• Tertiary (#333333): --alias-color-background-tertiary-default. Dark surfaces (e.g., snackbar contrast).
• Disabled (#cccccc): --alias-color-background-disabled-default.

Border / Separator

• Primary (#cccccc): --alias-color-border-primary-default. Standard component border.
• Primary Highlight (#e5e5e5): --alias-color-border-primary-highlight.
• Primary Active (#999999): --alias-color-border-primary-active.
• Secondary (#333333): --alias-color-border-secondary-default. Strong dividers.
• Disabled (#cccccc): --alias-color-border-disabled-default.

Overlay (modal backdrops)

• Weak (rgba(34,34,34,0.2)): --alias-color-overlay-weak.
• Middle (rgba(34,34,34,0.4)): --alias-color-overlay-middle.
• Mid Strong (rgba(34,34,34,0.6)): --alias-color-overlay-midStrong.
• Strong (rgba(34,34,34,0.8)): --alias-color-overlay-strong.
• Inverse Weak (rgba(255,255,255,0.2)): --alias-color-overlay-inverseWeak. White overlay on dark surface.

Icon (separate role from text — important for accessibility)

• Primary (#333333): --alias-color-icon-primary-default.
• Secondary (#cccccc): --alias-color-icon-secondary-default.
• Tertiary (#666666): --alias-color-icon-tertiary-default.
• Inverse (#ffffff): --alias-color-icon-inverse-default.

System (static)

• Static White (#ffffff): --alias-color-system-staticWhite-default.
• Static Black (#000000): --alias-color-system-staticBlack-default.
• Static Clear (rgba(255,255,255,0)): --alias-color-system-staticClear-default.

3. Typography Rules

Font Stack (verified live)

"Helvetica Neue", Arial, "Hiragino Kaku Gothic ProN Custom", "Hiragino Sans Custom", "Meiryo Custom", sans-serif

For non-Japanese locales the secondary stack adds Traditional Chinese support:

Helvetica Neue, Arial, "PingFang TC Custom", "Noto Sans TC Custom", "Microsoft JhengHei", "Hiragino Kaku Gothic ProN Custom", "Hiragino Sans Custom", "Meiryo Custom", sans-serif

The "Custom" suffix indicates Mercari runs optically-tuned variants of these system fonts in production — same families, adjusted spacing for marketplace UI density.

Weights

• 700: Primary CTAs, prices, badges, "Shop Now" hero CTAs, language toggles.
• 400: Default body, login/signup buttons, navigation links, secondary CTAs.

Verified: primary attention CTAs (e.g., "コンテンツにスキップ" skip link) use weight 700 with bg #ff333f and 4px radius. Secondary actions (login, signup, language) use weight 400.

Size Scale

• Base body: 15px (verified bodySize)
• Heading scale is application-defined (homepage uses 15-20px for H1/H2 with weight 700)
• Mobile sizes step down via --typography-*-font-size-mobile tokens

Conventions

• No letter-spacing tweaks — system defaults trusted.
• Default line-height ~1.4 (estimated from rendered metrics).
• Uppercase reserved for the "MERCARI" wordmark only.

4. Component Stylings

Buttons (verified across variants)

Primary attention CTA (red):

• bg #ff333f, text #ffffff, border-radius: 4px, padding: 11px 15px, font-weight: 700

Accent CTA (blue, e.g., "Shop Now"):

• bg #ffffff, text #0095ee, border-radius: 4px, padding: 8px 12px, font-weight: 700

Login / Signup (secondary, neutral):

• bg #ffffff, text #333333, border-radius: 4px, padding: 8px, font-weight: 400

Icon button:

• bg transparent, color #000000 or #333333, border-radius: 4px, padding: 4px, font-weight: 400

Language toggle:

• bg transparent, text #333333, border-radius: 4px, padding: 8px 16px, font-weight: 700

Cards (Product Card, Brand Card)

• White bg (--alias-color-background-primary-default)
• Subtle 1px solid #e0e0e0 border or no border (image-led cards)
• Brand thumbnails: border-radius: 50% (circular) — distinctive Mercari pattern for category navigation
• Image fills top, title + price below
• Price emphasis: weight 700, often in #ff333f (Mercari Red) for sale prices

Search Input

• Full-width bar at top of page, bg: #f5f5f5 (secondary surface), border-radius: 4px, dark gray placeholder #999999
• Camera search icon + magnifier icon inside the input on right

Navigation (top header)

• White sticky bg, height ~50-64px
• Mercari wordmark + heart logo on left
• Search bar centered
• ログイン (Login), 会員登録 (Signup), notification bell, language toggle (日本語) on right
• Tabs row below: おすすめ, マイリスト, ゲーム, etc. — horizontal scroll on mobile

Chips / Tabs

• Underline-driven active indicator (red underline #ff333f for active tab)
• Inactive tabs: text #333333 weight 400
• Active tab: text #ff333f (or #222222) weight 700 with 2px red underline

Snackbar / Toast

• Dark bg (--alias-color-background-tertiary-default: #333333)
• White text (--alias-color-text-inverse-default: #ffffff)
• Z-index --mer-z-index-snackbar: 1500

Modal / Dialog

• White surface, border-radius: 8px
• Backdrop: --alias-color-overlay-strong: rgba(34,34,34,0.8)
• Z-index --mer-z-index-modal: 1400

5. Layout Principles

Page Structure

• Max width: 1440px (--bqHLTv, --gIsGsE)
• Grid layout page padding: top 40px (--grid-layout-page-padding-top), bottom 64px (--grid-layout-page-padding-bottom), horizontal 36px (--grid-layout-page-padding-horizontal)
• Grid gutter: 24px (--grid-layout-gutter)
• Inner inset: 16px (--grid-layout-inset)

Spacing Tokens (semantic aliases)

Mercari uses Panda CSS-generated hashed token names alongside semantic aliases. Common values from CSS:

• 4px, 6px, 8px, 12px, 16px, 20px, 24px, 28px, 32px, 36px, 40px, 44px, 48px, 56px, 64px, 80px, 96px, 128px, 164px

This is a 4dp baseline scale extended with named tokens.

Density

Mercari is commerce-density — tight product grids with minimal card chrome, image-led visual hierarchy. The 6-column product grid on homepage uses ~190-240px card widths with 12-16px gutters.

6. Depth & Elevation

Mercari has explicit shadow tokens for floating UI:

• Card lift (subtle): 0px 2px 4px 0px rgba(0,0,0,.2) (--ljPKsT)
• Tooltip / popover: 0px 4px 8px 0px rgba(0,0,0,.2) (--coocrY)
• Modal / dropdown: 0px 8px 10px 0px rgba(0,0,0,.2) (--jcKRRc)
• Strong overlay: 0px 0px 16px 0px rgba(0,0,0,.2) (--gQVqIQ)

Z-Index Hierarchy (explicit named tokens)

• Menu: 1100 (--mer-z-index-menu)
• Navigation top: 1200 (--mer-z-index-navigation-top)
• Navigation bottom: 1200 (--mer-z-index-navigation-bottom)
• Autocomplete: 1300 (--mer-z-index-autocomplete)
• Dialog: 1400 (--mer-z-index-dialog)
• Modal: 1400 (--mer-z-index-modal)
• Side sheet: 1400 (--mer-z-index-side-sheet)
• Information popup: 1400 (--mer-z-index-information-popup)
• Action sheet: 1400 (--mer-z-index-action-sheet)
• Snackbar: 1500 (--mer-z-index-snackbar)
• Tooltip: 1600 (--mer-z-index-tooltip)

Animation

• Easing curves: cubic-bezier(0.65, 0, 0.35, 1) (sheets), cubic-bezier(0.33, 1, 0.68, 1) (snackbars/dialogs)
• Standard duration: 0.25s
• Loading spinner: 1.25s 8-step rotation

7. Do's and Don'ts

• DO use the --alias-color-* semantic tokens. The 681 variables cover virtually every UI surface — never hardcode hex values when an alias exists.
• DON'T invent new color values. Mercari's palette is exhaustive; if you can't find an alias, use the closest one.
• DO reserve Mercari Red (#ff333f) for the attention semantic — sale prices, danger actions, the brand mark, error states.
• DON'T use red for general "primary" CTAs that aren't attention-grabbing. Mercari's primary actions are often blue-accent (#0095ee) or neutral, not red.
• DO use weight 700 for primary CTAs and prices. Weight 400 for navigation, secondary actions, body.
• DON'T use weight 500 or 600 — they're not part of Mercari's typography rhythm.
• DO keep border-radius: 4px on buttons and cards. Mercari's commerce voice is sharp and functional.
• DON'T use pill-shaped or large-radius buttons — that breaks the marketplace density aesthetic.
• DO apply circular thumbnails (border-radius: 50%) to brand/category icons in navigation. It's a distinctive Mercari pattern.
• DON'T use shadows on flat product cards — let the white card on #f5f5f5 secondary bg provide separation.
• DO use the locale-aware font stack with Hiragino/Meiryo "Custom" variants. The optical tuning matters for Japanese readability.
• DON'T load custom web fonts. Mercari's audience is mobile-first across slow connections; system fonts respect that.
• DO use the explicit named z-index tokens (--mer-z-index-*) — Mercari's stacking order is deliberate.
• DON'T use arbitrary z-index values like 9999 — that breaks the layered system.

8. Responsive Behavior

Breakpoints (inferred from --typography-*-font-size-mobile tokens and --vbMobileBoundaryWidth-style patterns)

Touch & Mobile

• Mobile bottom navigation: tab bar with icon + label
• Form heights: small 36px, medium ~48px, large ~56px (estimated from spacing tokens)
• Touch targets: minimum 44px per Apple HIG conventions

Image Behavior

• Product images: square aspect ratio, 4px corner radius (matches button/card scheme)
• Brand thumbnails: circular (50% radius)
• Lazy-load via Next.js Image equivalent
• Placeholder skeleton uses --color-shimmer-bg / --color-shimmer-fg pattern

9. Agent Prompt Guide

Quick Color Reference

• Mercari Red (attention, sale, brand): #ff333f (--alias-color-background-attention-default)
• Accent Blue (links, info): #0095ee
• Success Green: #0aa466
• Decorative Yellow (ratings): #ffb818
• Primary text: #333333
• Secondary text: #666666
• Page bg: #ffffff
• Secondary bg: #f5f5f5
• Border default: #cccccc
• Inverse text: #ffffff (on dark surfaces)

Example Component Prompts

• "Create a Mercari-style attention CTA: bg #ff333f, white text, border-radius: 4px, padding: 11px 15px, font-weight: 700. Hover: bg darkens to #ff6574. Active: #e32b36. Use this for danger actions, sale CTAs, the brand-mark button — never for generic 'primary' actions (those use accent blue)."
• "Build a Mercari product card: white bg, no border or 1px solid #e0e0e0, 4px radius. Image fills top 70% in 4px rounded square. Title in 14px weight 400 #333333 (2-line clamp), price below in 16px weight 700 #333333 for normal price OR #ff333f for sale price. Optional sale badge in top-left corner using #ff333f bg + white text + 2px radius."
• "Design a Mercari brand thumbnail (category icon): circular border-radius: 50%, ~64-80px diameter, white bg with 1px solid #f5f5f5 border, brand image centered. Below: brand name in 12px weight 400 #333333, max 1 line ellipsis."
• "Create a Mercari search bar: full-width, bg #f5f5f5 (secondary surface), border-radius: 4px, padding 12-16px, placeholder #999999. Right side: camera icon + magnifier icon, both #666666. On focus: bg shifts to white, border becomes 1px solid #cccccc."
• "Build a Mercari snackbar: bg #333333 (--alias-color-background-tertiary-default), white text, border-radius: 4px, padding: 12px 16px, fixed at bottom with z-index 1500. Slides in via cubic-bezier(0.33, 1, 0.68, 1) over 0.25s. Auto-dismiss after 3-4s."

Iteration Guide

1. Always reference --alias-color-* tokens, not raw hex. Mercari's 681 vars are the canonical source.
2. Mercari Red (#ff333f) is the attention role — destructive, sale-emphasis, brand mark. Not a default primary.
3. border-radius: 4px is the workhorse. Cards, buttons, badges. Brand thumbnails get 50% (circular).
4. Weight 700 for prices and primary CTAs, weight 400 for everything else. No middle weights.
5. Use the locale-aware font stack with Hiragino/Meiryo "Custom" variants. Optical tuning matters.
6. Z-index uses named tokens (--mer-z-index-*) — never arbitrary numbers.
7. Animation easing cubic-bezier(0.65, 0, 0.35, 1) for sheets, cubic-bezier(0.33, 1, 0.68, 1) for snackbars/dialogs. Duration 0.25s.
8. Surface contrast (#ffffff cards on #f5f5f5 page bg) handles separation — minimal shadow needed on flat layouts.
9. Body text #333333, secondary #666666, tertiary #999999 — three-tier text hierarchy across the entire system.
10. Page padding 36px horizontal, 40px top, 64px bottom, with 24px gutter — the layout grid is explicit.

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10. Voice & Tone

Mercari's voice is pragmatic, transparent, and functionally-warm — the voice of a trust infrastructure, not a lifestyle brand. Where LINE sells belonging ("Life on LINE") and where Apple sells aspiration, Mercari sells circulation: moving value from someone who no longer needs it to someone who does. The copy reflects that — action verbs, concrete amounts, shipping logistics, and a Japanese-origin register that favors politeness without ceremony. The "Move Fast" value is balanced by "Safe Rollout" — safety copy is direct ("ID verified", "payment held until delivery"), never reassurance-only ("don't worry!").

Forbidden phrases. "Revolutionary", "game-changer", "world's best", "amazing deals". In Japanese UI: avoid カタカナ tech-marketing language (イノベーティブ, ディスラプティブ). Generic hype emoji (🔥 ✨ 💯 🚀) on listings or system copy — emoji is reserved for user-generated message content between buyer and seller, not for platform voice.

Representative voice samples. Where a verified live string exists on Mercari's public surfaces it is cited with a source marker; where no public surface carries the string (logged-in-only copy, error states), the sample is marked illustrative and a production team should replace it with Mercari's real live copy before shipping.

• Primary JP nav label (verified): "出品" — two-character imperative, the canonical "List item" tap target across the app.
• JP footer safety banner (verified): "メルカリあんしん・あんぜん宣言！" — exclamation-ending, commits to a publicly-listed safety initiative rather than generic "trust".
• EN product description (verified): "A C2C marketplace where individuals can enjoy buying and selling items. Through our unique payment deposit system and our use of AI to monitor for fraud, anyone can enjoy safe and secure transactions." — tone exemplar: concrete mechanisms (payment deposit system, AI to monitor for fraud) over vague reassurance.
• Empty state (new user, no listings): "Nothing listed yet. Take a photo and list your first item."
• Error (photo upload failed): "Upload failed. Tap to retry."
• Success (item sold): "Sold to . Package it and print the shipping label."

11. Brand Narrative

Mercari was founded February 2013 in Tokyo by Shintaro Yamada (山田進太郎) — born in Seto, Aichi Prefecture; Waseda University mathematics graduate; previously founded the gaming company Unoh in 2001 which was acquired by Zynga 2010 (Shintaro Yamada — Wikipedia). Yamada left Rakuten Auctions and travelled the world asking one question — "What can I do to help society thrive with the finite resources we have?" (about.mercari.com). That question became the company's founding premise: circulate all forms of value to unleash the potential in all people. The answer took the shape of a smartphone-first C2C marketplace that made listing an item fast enough (3 minutes, 3 photos) to be worth doing for a single pair of used jeans.

From that origin Mercari grew into Japan's largest C2C marketplace (50M+ downloads, 350K daily listings ), expanded to the US in 2014 and UK in 2016, became Japan's first tech unicorn (>$1B) in 2016, then completed a Tokyo Stock Exchange IPO June 2018 raising over $1.2B — making Yamada Japan's newest billionaire (The Japan Times — Mercari IPO 2018). U.S. operations achieved profitability for the first time fiscal-year ending June 30 2025. Spun up adjacent divisions: Merpay (2019, payments — "Building trust for a seamless society"), Mercoin (2023, crypto — "Circulate your value, anywhere and everywhere"). The consistent thread across divisions is the word circulate — not sell, not exchange, not marketplace. Every product framing returns to that verb.

What Mercari refuses: the auction-complexity aesthetic of eBay (bidding clocks, snipe warnings); the spam-forward commerce chrome of flash-sale marketplaces (flashing banners, permanent 50%-off overlays); the corporate-blue sterility of legacy Japanese e-commerce (Rakuten Ichiba, Yahoo! JAPAN Auctions). What it embraces: a semantic-token-first design system (681 :root variables — see §2), Mercari Red as a finite attention signal (never decorative), mobile-first listing flow, and explicit trust infrastructure (ID verification, escrow, ratings) surfaced directly in the UI rather than hidden in settings.

12. Principles

1. Circulate, don't just sell. Product framing uses the verb circulate; listings flow from one user to another, not from a retailer to a consumer. UI implication: both sides of a transaction are peers — no "seller dashboard" / "customer account" asymmetry. The same person is often both on the same day, and the interface reflects that symmetry.

2. Semantic tokens are the source of truth. All 681 :root CSS custom properties (--alias-color-background-attention-default and friends) resolve through the token layer before any pixel is painted. UI implication: components never hardcode hex values. A theme swap (dark mode, regional variant) is a :root redefinition, not a UI refactor.

3. Mercari Red is the attention role, not a primary accent. #ff333f signals danger, sale emphasis, and the brand mark — nothing else. Using it as a decorative accent on buttons, illustrations, or empty-state icons dilutes its function as a warning signal. UI implication: primary CTA surfaces use neutral dark text on white, not red; red is reserved for destructive actions and sale-price emphasis.

4. 4px radius is the commerce signature. Sharp 4px corners read as "browse the catalog efficiently" — LINE's 50px pills would make Mercari feel social when it is transactional. UI implication: never round corners to match a reference aesthetic ("softer", "friendlier"); the 4px is intentional functional rigor.

5. Two weights: 700 and 400. Nothing in between. Price, badge, primary CTA, and section headings use 700. Body, secondary labels, and helper text use 400. Middle weights (500, 600) are absent — they blur the hierarchy between scan-value (price, button) and read-value (description). UI implication: disable imported fonts' "medium" weight; design tokens expose only two.

6. Hiragino / Meiryo "Custom" variants are first-class, not fallbacks. The optically-tuned Japanese faces are the primary reading surface for 50M+ Japanese users; they lead the stack, not end it. UI implication: never specify -apple-system or system-ui alone — the fallback chain must name the Japanese optical variants explicitly (verified at runtime on jp.mercari.com).

7. "Move Fast" pairs with "Safe Rollout." The engineering culture (Go Bold, All for One, Be a Pro, Move Fast — careers.mercari.com/mission-values) is explicitly paired with documented-failure practice. Blog titles like "Safe Chunked Execution" and "Behind the Scenes" are intentional; failures are surfaced, not buried. UI implication: error and recovery states are visible on the failing element ("Upload failed. Tap to retry"), not hidden behind a modal or a support ticket.

8. Disagree & commit. Once decisions are made — after debate — the team commits fully (mission-values). UI implication: there is no "legacy styles" escape hatch in the design system. Deprecated tokens are removed on a schedule, not left for "gradual migration forever."

13. Personas

Personas are fictional archetypes informed by publicly described Mercari user segments and mission documentation; not individual people.

Yuki Sato, 28, Tokyo. Office worker who declutters every 2–3 weeks — a jacket, a manga set, a hand mixer. Lists in under 3 minutes during her evening commute and expects the "sold" notification to tell her exactly how to ship. Japanese-language-first; sub-¥20,000 items only, rarer collectibles still go to Yahoo! Auctions.

Takeshi Nakamura, 42, Osaka. Secondhand-bookshop owner using Mercari as a secondary retail channel — photographs overstock at the shop, lists in the evening. A 1-star rating materially damages his shop's income, so he treats the platform's forced taxonomy (Like New, Good) as a feature that protects him from subjective disputes.

Sarah Kim, 19, Los Angeles. Mercari US user since 2022; thrifts Y2K fashion and old consumer electronics. Never uses eBay ("too auction-y, too slow"); compares Mercari to Depop and picks Mercari for lower-budget finds, Depop for curated vintage.

Hiroko Tanaka, 56, Kobe. Retiree selling handmade knit goods — supplemental income that Yahoo! Auctions' complexity never allowed. Depends on the ID-verification badge as social proof; buyers hesitate on higher-priced items without it. Her listings are spare — 3 photos, 2 sentences, 1 honest condition label.

14. States

Copy strings below are illustrative treatments of Mercari's tone applied to each state, not verified live copy. A production team should replace them with Mercari's actual copy (observable via Playwright against jp.mercari.com's logged-in surfaces) before shipping.

15. Motion & Easing

Mercari's motion vocabulary is disciplined commerce motion: fast feedback on interaction, measured confirmation on completion, no spring or bounce. This is deliberate. Spring motion reads as delight; commerce requires precision about amounts and states. LINE's ease-sticker overshoot would be wrong here — a Mercari user watching a purchase-confirmation animation should feel confidence, not whimsy.

Durations:

Easings (verified from live :root computed styles on jp.mercari.com):

No ease-bounce, no ease-overshoot, no cubic-bezier with y-values > 1 or < 0 anywhere in the system. Commerce has no spring.

Signature motions.

1. Card tap feedback. Listing cards scale 1.0 → 0.98 over motion-fast on press, returning to 1.0 on release. Subtle, thumb-oriented, feels tactile without bouncing.
2. Bottom sheet rise (filters, sort, category picker). Uses ease-sheet over motion-standard. The deliberate easing matches the Japanese-origin UX tradition of drawers sliding smoothly, not snapping into place.
3. Favorite toggle. Heart icon fills over motion-fast with a simple crossfade — no scaling pulse. The commit is the signal; no decorative reinforcement.
4. Listing submit success. Full-width success banner fades + slides down from top at motion-slow with ease-standard. No confetti, no illustration — the ship-now CTA that appears is the reward.
5. Reduce motion. Under prefers-reduced-motion: reduce, all motion-* tokens collapse to motion-instant. Sheets and modals appear via opacity only. The app remains fully functional; motion is never load-bearing for comprehension.

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Verified: 2026-05-08 (omd:migrate run 35 — Apple-tier) Tier 1 sources: jp.mercari.com home + /search (live DOM via playwright — Primary #ff333f Mercari Red 4px / 11×15 / 45px / 15px·700 BOLD; Outline #fff 4px / 36px / 14px·400 / #333 Charcoal; search filter chip 18px / 4×8 / 36px / 14px·400; category tab 0px / 14px·700 active-state Red shift; US promo accent #0095ee Bright Blue cross-border-only). Tier 2 sources: styles.refero.design / getdesign.md — no record. Tier 2 (Philosophy/founders/IPO): Wikipedia (Mercari + Shintaro Yamada), Japan Times (2018-06 IPO Yamada billionaire), Bloomberg, BoF 500, Crunchbase, about.mercari.com. Style ref: line (JP East-Asian, retained). Conflicts unresolved: none. Earlier addition: filter pill 18px sub-tier + US-locale Bright Blue #0095ee cross-border accent were missing from prior pass.