One Piece: Grand Adventure

Unlock Eneru (Crocodile's adventure mode):
Get Eneru as your ally in the Jaya area and win a battle using him.

Unlock Mihawk (Chaser's adventure mode):
After recruiting Mihawk win a battle using him.

Unlock Mr. 2 Bon Clay (Crocodile's adventure mode):
Get Mr. 2 as your ally and win a battle using him.

Unlock Nico Robin (Luffy's adventure mode):
Get her as your ally at the end and win a battle using her.

Unlock Ohm (Crocodile's adventure mode):
Get Ohm as your ally in the Jaya area and win a battle using him.

Unlock Shanks (Buggy's adventure mode):
Recruit Shanks and then win a battle using him.

Unlock Trace (Buggy's adventure mode):
Recruit him in Drum Island then win a battle using him.

 