Kouji Koike focused on enhancing code quality and maintainability in the flowplayer/hls.js repository by refactoring the adaptive bitrate logic. He extracted the nextAutoLevel calculation into a protected deriveNextAutoLevel method within the AbrController, ensuring the existing behavior remained unchanged while improving code organization. This TypeScript-based refactor decoupled the calculation from its call sites, making the logic more readable and easier to test or extend in the future. By isolating this functionality, Kouji reduced complexity and risk in future updates, laying a foundation for safer performance improvements and more robust unit testing without introducing new features or bug fixes.