Interactive & Playableインタラクティブ & プレイアブル · Designer & builder
Overview概要
Tic-tac-toe with one rule changed — a 4×4 board, two marks a turn — playable solo, against an AI, or online with a second phone.○×を一部変え、4×4・1 手 2 個置き。1 台でも AI 相手でも、2 台でも遊べる。
My part担当
- Co-invented the 4×4, two-marks-per-turn rule with his son over hundreds of rounds on paper and notes apps
- Built one board that works face-to-face, against an AI opponent, and online
- Built the Gemini-first AI opponent with a local-search fallback across 4 difficulty levels
- Wrote the QR/code pairing, presence, and rejoin logic that became the starting point for the separate Snap Pair library
Marubatsu 2.0: Online 4×4 tic-tac-toe
A four-by-four board where you place two marks per turn and four in a row wins. Invented with my son on a school commute ferry, shipped as a real-time multiplayer arena with an adaptive AI adversary.
- 1
- Core rule changed: 2 marks a turn on a 4×4 grid
- 3
- Ways to play: Solo pass, AI opponent, or QR scan
- 9
- Localized languages with zero setup required
- <100ms
- Peer board synchronization via Firebase RTDB
The rule is the asset; the app is disposable.
Tic-tac-toe was solved centuries ago, but placing two marks on a 4×4 grid revives tension instantly. The exact same ten win lines power the local game, the AI search tree, and the room referee.
Instant pairing without accounts.
Creating a room gives a 6-character shortcode and a QR code. The second phone scans and is in. No logins, no downloads, and the server only arbitrates the state.
Gemini-first adaptive adversary.
The AI opponent uses Gemini to generate playful contextual banter and tactical moves across four difficulty settings, falling back seamlessly to an offline search engine when network drops.
Where it belongs
- Two people with five minutes: Waiting lounges, trains, cafes — pull out one phone or scan between two, with zero explanation needed.
- Shared-board engine pattern: The lightweight pairing engine built here evolved into Snap Pair, enabling any quiz, voting board, or party game across phones.
- Multi-platform responsive web: Plays equally well on touch screens, trackpads, and desktop browsers with full keyboard accessibility.
My Contribution
- Co-invented the 4×4 two-marks game mechanic over hundreds of rounds
- Designed complete UX/UI, board iconography, and tactile micro-interactions
- Engineered the Next.js 16 and Firebase RTDB real-time pairing architecture
- Integrated Gemini AI adversary with offline heuristic fallback
Collaborators & Heritage
- Co-designed with Takao's son on the school ferry commute in New York
- Original rule tested on paper napkins before writing a single line of code
- Released as open-source web application under Creativity Is Everywhere LLC