A 3D browser game where every monster is a Japanese word

The game. You roam a procedurally generated island in third person — keyboard on a desktop, an on-screen joystick and A button on a phone. Five biomes (meadow, forest, lake, volcano, snowy peak) each hold their own species at their own level range. Walk into a wild monster and a turn-based battle starts, with eight elements and a type chart deciding what lands hard and what fizzles. Weaken it, throw a Kotodama Orb, and it joins the party. Six missions and a twelve-entry KotobaDex give the roaming a shape, including one deliberately elusive species — the moon rabbit ツキウサ, at a 15% base catch rate against a starter's 40%.

Learning is a move, not a screen. The vocabulary quiz is one of the actions available on the battle menu, once per fight. Get the word right and the catch chance goes up by a flat 0.25 — for scale, wearing a monster's health all the way down is worth 0.55, so a correct answer is worth about the same as taking 45% of its HP off, and it pays 25 points on top. Answering well is a genuine alternative to fighting well, which is the only way to make a learning mechanic matter. The bank is 36 words — the twelve monster names plus everyday vocabulary — asked in both directions, Japanese to English and back.

Three subtitles at once. Every spoken line shows the Japanese, the romaji reading and the English meaning simultaneously. A learner can hear the line, look at the kana, check how it is pronounced and confirm what it means without leaving the screen — the scaffolding that makes the game usable by a genuine beginner rather than only by someone who already reads Japanese.

Voice with no API bill. The 31 Japanese voice lines were generated once by a self-hosted Kokoro text-to-speech model running on the same server — a female voice for Professor Sakura, a male one for the narration — and written out as static MP3s alongside a generated manifest carrying all three subtitle rows per line. Nothing is billed per use, no text leaves the box, and there is no runtime dependency that can rate-limit or disappear. The music is generated too: the background tracks are a WebAudio step sequencer with separate roam and battle moods, so beyond the voice-over there are no audio files at all.

No build step, on purpose. Three.js 0.178 is vendored into the project and the rest is vanilla JavaScript using native ES modules — ten files, 2,821 lines. No bundler, no transpiler, no CI step to keep green: the files that are written are the files that ship, and they will still run years from now without a toolchain to resurrect. The visuals are procedural in the same spirit — terrain, monsters and trainer are all assembled from primitives in code rather than modelled in an external tool, so there are no art files to license or keep in sync. The only third-party thing loaded at runtime is the Japanese display webfont.

Cache discipline as a feature. Deploying is a file copy and a cache purge, but a CDN caches by file extension, so a half-purged deploy once served a stale module while a direct fetch of the same URL showed fresh bytes. The rule now is that every relative import and the stylesheet carry the same version query, bumped on every deploy and never reused. The version badge in the corner of the screen is derived at runtime from the loaded module's own version query — so a stale badge means a stale deploy, by design, and the game reports its own cache bugs.

Testable from the outside. An automated browser evaluates its scripts in an isolated JavaScript world where the page's own globals are invisible, but the DOM is shared. So the game exposes a small #e2e element: one attribute publishes the live game state as JSON, another accepts commands. That is what lets an unattended agent start a new game, skip the voiced intro, pick a starter, walk into a monster and check the result — the screenshot on this page was captured through that bridge.