Building a Sarcastic AI English Tutor with Persona-as-Code and Gemini Audio Input for Pronunciation Correction

I built a niche AI English conversation app called Mesugaki AI English on Kotonia. "Mesugaki" (メスガキ) is a tsundere-style bratty persona popular in Japanese subculture — imagine a character who constantly mocks you but secretly has your back. At first glance this looks like a one-off gag product, but under the hood it's a two-layer design: persona managed as code + Gemini audio input for actual pronunciation correction. This post covers those design decisions and the rough edges I hit, from a sol...