まるかいてドカン!
A free doodle tower defense on notebook paper: draw circles for cannons, lines for walls and triangles for mines to stop marching stick figures. The developer says it was made with Opus 5.5 and that the first version ran after a little over an hour.
Official site soyukke.itch.io, verified Nov 3, 2026. Linked as the browser version (ブラウザ版) in the developer's Zenn article.
Where to play
Every platform this game is on. Links are checked against official sources; we never host or mirror games.
- Play free — itch.ioitch.ioReleasedFree
Plays in the browser on itch.io. No download.
Browser (no download) · Mobile · Official link verified Nov 3, 2026.
- Coming soon · SteamSteamComing soon · Steam version listed as coming soon; the store page describes online matches with 2–8 friendsPaid
Download through the Steam app. A free Steam account is required.
Desktop · Steam
About まるかいてドカン!
まるかいてドカン! (Maru Kaite Dokan!, roughly "draw a circle, boom!") is a free tower defense game played in a desktop or phone browser, in which what you draw becomes your defences. Stick figures march across a notebook page toward your base, and you stop them by drawing: a line becomes a wall, a circle a cannon, a triangle a mine, a zigzag lightning and a square ice. The strokes you draw become the actual bodies of the defences, so neat shapes are strong and messy ones keep their quirks, such as a potato-shaped cannon or a squishy wall. After each wave you pick one of three upgrade cards; there are 30 waves and then an endless mode, and the damage numbers keep climbing. Drawing shapes in unusual ways reveals 16 hidden discoveries. On a phone you draw with a finger in landscape and hold a defence to inspect or erase it; on a computer you draw with the mouse and use keys for waves, speed, a tracing pen and the upgrade cards. Japanese and English can be switched on the title screen. The developer, soyukke, an office worker who makes games as a hobby, lists it in a Zenn article as made with Opus 5.5 and published on 26 Sep 2026, and says the idea had been given up in March 2026 until the first version, built with Opus 5.5, was running after a little over an hour. A Steam version is listed as coming soon; its store page describes online matches with 2–8 friends who send their drawn "masterpieces" into each other's notebooks. Free on itch.io.
Screenshots and art
まるかいてドカン! key art · Steam store artwork
How it was built
Partially verifiedIn a Zenn article (Japanese, 11 Oct 2026) about the two weeks after Claude Opus 5.5 came out, the developer's timeline lists 「まるかいてドカン!」 as made with Opus 5.5 (Opus 5.5で作った) and published on 26 Sep 2026. The developer writes that the game was an idea given up in March 2026 and that, after asking Opus 5.5 again, the first version was running after a little over an hour. Writing about games made this way, the developer says they cannot claim "I made it", but that "the AI made everything" is also wrong, because the idea of what the game should be is the developer's own; the developer's part is looking at the result and saying when it is wrong. The article is tagged Claude and Claude Code, and the developer counts themselves among office workers who make games with Claude Code, but it does not say which app was used for this game or how much of the code AI wrote.
Prompt-driven development with Opus 5.5, per the developer: an idea dropped in March 2026 was handed to Opus 5.5 again and had a first working version in a little over an hour. The developer describes their own role as deciding what the game should be and rejecting what goes against it. Built in Godot 4.6, per the credits on the itch.io page, which also list the DotGothic16 (SIL Open Font License 1.1) and PixelMplus12 (M+ FONT LICENSE) fonts. The upcoming Steam version adds online play for 2–8 players and 11 interface languages.
- Engine / framework
- Godot 4.6
- Languages
- Not disclosed
- Team size
- 1 (solo)Developer ReportedZenn (soyukke)
- Initial build time
- A little over an hour to a first working versionDeveloper ReportedZenn (soyukke)
- Development time
- Not disclosed
- Development cost
- Not disclosed
- AI-written code
- Not disclosed
“Opus 5.5に頼み直したら、最初の版は1時間ちょっとで動きました。”Verification notes: AI use, the release date and the build time come from the developer's Zenn article (published 11 Oct 2026, updated 12 Oct 2026), which links both the itch.io browser version and the Steam page; the itch.io page ticks AI Assisted and Code. Gameplay, controls, languages and credits from the itch.io page; the itch.io rating of 5.0 rests on 2 ratings. Team size 1 rests on the article's statement that, with Opus 5.5, the developer could handle development, replies to comments and promotion of the hobby games alone. The Steam version (app 5342290) is a different, multiplayer design and is listed as coming soon with no price; its AI disclosure covers art, music, sound effects and draft translations. Nothing in the sources describes AI used during play. The game was not played. No location is given.
Development history
- March 2026
The developer gives up on the idea once, per the Zenn article.
DeveloperZenn (soyukke) Published, after being remade with Opus 5.5, per the developer's timeline; it drew responses on X.
DeveloperZenn (soyukke)
Game performance
Each figure measures something different — concurrent players, owners, downloads and sales are never interchangeable and are never added together. Labels show where each number comes from.
itch.io
Free in desktop and phone browsers (HTML5); phones in landscape.
Not publicly available: Gross revenue.
Steam
No price listed on Steam (store API checked with cc=us on 4 Nov 2026). Windows only.
No public metrics recorded for this listing.
Not publicly available: All-time peak concurrent players, Concurrent players, Steam reviews, Positive Steam reviews, Estimated owners, Copies sold, Gross revenue.
Sales & revenue (all platforms)
Browser game — there are no downloads to count.
Reviews & rankings
Not yet reviewed by our editors.
Sources
| Source | Type | Published | Accessed |
|---|---|---|---|
| Opus 5.5はディソードだ。全人類ギガロマニアックス時代に、ギュられたらギュり返せ Zenn (soyukke) · Japanese | Devlog | Oct 11, 2026 | Nov 3, 2026 |
| まるかいてドカン! / Maru Kaite Dokan! by soyukke itch.io · Japanese | Store page | Not confirmed | Nov 3, 2026 |
| Maru Kaite Dokan! on Steam Steam | Store page | Not confirmed | Nov 3, 2026 |
