You need not bother delving into the game lore. This rp was inspired by KH but it's not deeply integrated into the games or anything like that. The borrowed ideas are all drawn from the early games - nothing really past KH2. Mostly just basic concepts like hearts, heartless, nobodies, light, darkness, worlds, keyblades, etc. So there is no Master of Masters to worry about. 

And adult characters are fine! Let me know if you have any concepts you want to run by me.