Get ready for a grindy grind
...
Max level for 1 character is 175. May seem pretty straight forward...HOWEVER, in order to max out just one character
NEARLY EVERY OTHER CHARACTER NEEDS TO BE LEVELED TO A CERTAIN POINT. For example, before Ichigo can branch off into Kenpachi's tree, Kenpachi needs to be level 9.
This eliminates a straight grind for one character.
I did mine with Stark for 1 reason: He is crazy easy to use and build an insane hit counter with. The guy is seriously a combo machine.
I took him into Beat Attack (beginner) at ~60, and just went nuts for 3 mins. I ended just about every run with 3000 to 3500 soul points.