Easy
Enemies die with a few hits, even if your character is just starting out.
Normal
Enemies are at standard strength, but Level 100 characters will have an easy time.
Hard
Enemies are geared to Level 100 and maximum status play. Extra zombies spawn to attack you during boss fights.
Violent
Enemies are rigged to kill you with as few hits as possible. Like hard, extra zombies appear during boss fights.
Berserk
Enemies only drop red experience orbs; Aya and Saki instantly enter Rampage Mode and cannot return to normal. Red experience orbs gain the ability to refill your characters' vitality while rampaging. Enemies otherwise similar to violent difficulty.