I'm seeing one huge problem here. For an RP based around 'character interactions and building', your drastically limiting character build options for the sake of pvp 'balance' and making everything super watered down and boring in the process.

I mean, sure if you just want a hunter x hunter sorta thing going, then just say that. But then nein can be used to an extent that is very close if not exactly magic. (Greed island) or borderline alchemy (Chimera Ants) so it seems like that isn't even happening here. 

I dunno, just seems like the initial vision, then your refinement of that vision, are two totally different ends of the spectrum. Aren't shonen anime supposed to be fun and over the top? Fist of the North Star being a great early example. Or bobobo, if you want a shonen parody. (I miss that one.)

If your super worried about PvP being unbalanced, you can always just make death an inconvenience instead of a certainty with dragonballs or something. Its not going to happen very often if your trying character development stuff anyway.

OR, and here me out here. Go One Punch Man and just have everything dialed up to 11.