Simply finish the Single player mode in Normal difficulty to unlock the Hard mode.
Very Hard difficulty
You'll have to finish the Single player mode in Hard difficulty to unlock the Very Hard one.
Time Attack Mode
Beat the game with Very Hard difficulty.
Gallery mode
Beat the game once with any character.
Easy Win : Kakashi
When you start a battle using kakashi, press Down + Triangle Kuchiyose: Doton: Tsuiga no Jutsu (Tracking fang jutsu) then quickly charge your Raikiri (Lightning blade) to the max then the victim(s) will K.O.
See more:
Battle Stadium D.O.N Video Game Console Items...
