In case you don't have a save game from "Naruto Hero 3" in your memory card, you can unlock secret characters by performing the stated tasks.

Unlockable	How to unlock
Gaara (old version)	On "Hero Mode", defeat his nearly full Shukaku version using Naruto.
Godaime Hokage (Tsunade)	On "Hero Mode", unlock the scene where she attacks Orochimaru.
Haku	Defeat him in "Hero Mode"
Jiraiya	On "Hero Mode", unlock the scene where Naruto protects Tsunade from Kabuto.
Kabuto	On "Hero Mode", defeat him using Naruto.
Kankurou (old version)	On "Hero Mode", unlock the scene of his fight against Shino during Konoha's Invasion.
Nidaime Hokage	On "Hero Mode", unlock the scene of Sandaime's funeral.
Orochimaru	Playing "Hero Mode", you get him in the level after Naruto fights him.
Sandaime Hokage	On "Hero Mode", defeat Orochimaru using him during Konoha's Invasion.
Shizune	On "Hero Mode", unlock the scene where Tsunade attacks Orochimaru.
Temari (old version)	On "Hero Mode", unlock the scene of her fight against Shikamaru during the Chuunin Exams.
Zabuza	Defeat him in "Hero Mode"