well...technically...there are no "evil" characters, just different factions of races.... and i am going to do some research on heartless types... and youll get to choose the race....like heartless for example...but i like your leveling system...so im going to incorperate it into leveling...but i am going to add classes as you level up and according to what you level up... for example
the base class for heartless is a shadow....
but if you level his strength up to lets say (not official) 5...then you turn into a soldier.... so youll get the abilities and stat boosts of that class...but if you level up your magic to 5 instead... you will become a requiem... and there will be defense and speed levels also...but ill also include combonations stat forms...such as leveling a shadows magic to level 5...and so on and so on....
but be aware that when you change your form your stat gauge will decrease but you will keep the stat boosts from the previous gauge...for example...let say that your last gauge for your shadow was
str-5
mag-2
def-4
speed-1
and then you turn into a soldier...despite abilities to use a stat exchange...(you know...more strength for less spead or something) you will still have all the stats...but with your rank you will gain new abilities for your class.... i hope you understand this because i am typing as i am thinking up this stuff