This is the leveling system:
F class~ Level 15-20> Can defeat F rank monsters; total stats equal up to 200
E class~ Level 21-30> Can defeat E rank monsters; total stats equal up to 300
D class~ Level 31-40> Can defeat D rank monsters and E ranked Demons; total stats equal up to 400
C class~ Level 41-50> Can defeat C rank monsters and D ranked Demons; total stats equal up to 500
B class~ Level 51-60> Can defeat B rank monsters and C ranked Demons; total stats equal up to 600
A class~ Level 61-75> Can defeat A rank monsters and B ranked Demons; total stats equal up to 750
S class~ Level 74-89> Can defeat S rank monsters and A ranked Demons; total stats equal up to 900
Ex class~Level 90-99> Can defeat SS ranked monsters and S ranked Demons; Four stats are up to 999
RoB class~Level 100+> unknown
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