KPDH Rhythm Runner

Inspiration

I've always wanted to make games, but the barrier to entry felt too high. Learning an engine through hours of Udemy courses, programming gameplay systems, and creating a polished game as a solo hacker was a big ask with limited free time.

Codex changed that. Instead of getting stuck on implementation details, I could focus on learning by building. The project also became personal: I wanted to create a simple rhythm-action game that my daughter would genuinely enjoy playing, making the project rewarding regardless of the outcome.

Gaming is also a great gateway to technology. If this project helps inspire a future girl coder, it will have been worth it.

What it does

KPDH Rhythm Runner is a rhythm-action game where every jump, attack, dodge, and obstacle is synchronized to the music. Each level is driven by a beatmap that choreographs gameplay around a song, turning the music into the core game mechanic.

How we built it

KPDH Rhythm Runner is built in Unity using C#. I used Codex throughout development, with GPT-5.6 acting as my programming partner to implement gameplay systems, debug issues, explain unfamiliar APIs, and rapidly iterate on mechanics.

Development became a cycle of designing an idea, implementing it with Codex, testing it in Unity, and refining it until it felt right. GPT-5.6 also became an unexpected sounding board for game design and even for improving how I prompted Codex, creating a feedback loop that significantly improved my development workflow.

Challenges we ran into

The biggest challenge wasn't writing code--it was finding the right tooling and content pipeline.

I learned that effective agentic development depends heavily on the surrounding ecosystem. It wasn't enough to have a capable coding agent; I also needed to assemble the right building blocks. That meant finding compatible asset packs, learning how to animate meshes with Mixamo, integrating third-party character controllers and visual effects, and understanding how all of those pieces fit together inside Unity.

Another important lesson was that tooling constraints matter. Although I knew Macs weren't ideal for desktop game development, I discovered that headless Unity and Unreal workflows weren't mature enough for the agentic workflow I wanted. I quickly ran into a wall. Without reliable headless execution, Codex couldn't effectively inspect, modify, and validate the project. Moving to a Windows development environment unlocked a much smoother development loop.

I also began with the goal of procedurally generating infinite rhythm levels from any song. While much of the pipeline could be automated, I ultimately learned that the final layer still required human craftsmanship. Rhythm games aren't just synchronized to music—they're choreographed for the player.

Accomplishments that we're proud of

The biggest accomplishment was fulfilling a childhood dream of shipping a game.

More importantly, I built something uniquely for my daughter. AI made it practical to create bespoke software that didn't need to be commercially viable to be meaningful. If it inspires her to become a creator herself someday, that's a win.

What we learned

This project taught me that AI doesn't eliminate the human element. It amplifies it.

Codex handled much of the implementation work, but the creative decisions remained mine: choosing mechanics, selecting assets, and continually refining the experience. Most importantly for a game, I was still responsible for deciding what felt fun and what evoked emotion.

For me, that's the most exciting part of agentic coding. AI lowers the barrier to creating software, but the vision still comes from the developer. The agent can help build the game, but the human brings the taste, creativity, and ultimately the soul.

What's next for KPDH Rhythm Runner

In the short term, I'd like to expand the beatmap system with additional songs, improve enemy encounters, and continue refining the gameplay.

More broadly, I want to continue exploring how AI enables bespoke software. KPDH Rhythm Runner wasn't built to start a company—it was built because AI finally lowered the barrier enough to create something deeply personal. I think that's one of the most exciting opportunities these tools unlock, and I'd love to continue exploring where that leads.

Built With

• codex
• gpt-5.6
• unity