@phoenixfire, excellent feel free to tinker as you wish!
@PsionicFox, I am very hesitant of homebrew things, as I already think it is difficult to keep power somewhat balanced among the group, and homebrew allows another place for power differences to get out of hand. That said you can certainly ask. Its easier if it correlates to other examples in the game, but I understand that makes it hard to make new unique things.
@Madhatter, I don't think that I have come across that yet hehe, as I said I'm partway through the show and don't get the manga. But if its rank 15 stuff it's far off in the distance, so we're okay!