learning Japanese rpg? like an rpg that's designed to help you learn Japanese?
Yeah, the first one came out called "Learning Japanese To Survive - Hiragana Battle" and it teaches you how to learn and write hiragana. It's done with RPG Maker I think, but it's like an old Final Fantasy game where there's a villain and the things you fight are the hiragana characters and the only way to damage them is to use what they are called as the attack. In between battles you learn new stuff and even learn some simple common words and such, some of which use the hiragana you learn. I honestly haven't put enough time into it to say that I learned a ton, but it's meant to be a fun stepping stone into the language. Once things settle down for me, I plan to go back to it.
The newest one is Katakana War and you can tell what it teaches. That's the one I kickstarted, even having not finished Hiragana, just because it seems like an interesting idea to support.