You can now use all members of the Akatsuki.

You've acquired S Rank in "Earth Shatter".

You've cleared Chapter Six.

You can now use Jiraiya, Tsunade and Orochimaru.

You've acquired S Rank in "The Two Uchiha".

You can now use Sasuke, Suigetsu, Karin and Jugo.

You've acquired S Rank in "Sturm und Drang".

You've acquired S Rank in "Showdown Between Best Friends".

You can now use Kakashi, Yamato, Guy and Asuma.

Beat the game.

Collect all Battle Stamps.

Acquire the Pumpkin Costume.

Defeat Metxel in battle.