Follow instructions to unlock new characters:

Character	How to Unlock
Deidara	Complete sidequest 2 - Instead of going South to find Sai, go East, then North-West to find Shino. He will give you sidequest 2
Four Tail Kyuubi Naruto	Clear all 30 floors of Exploration Mode with all 10 characters on normal difficulty.
Hoshigaki Kisame	Complete sidequest 1 - see Uchiha Itachi
Kabuto	Win 15 battles in Survival Mode
Legendary Sannin	Win 15 battles in Survival Mode
Non - Shippuden Characters	Win 15 battles in Survival Mode in difficult
One Tail Kyuubi Naruto	Complete story mode in difficult
Sasuke (s)	Beat story on any difficulty
True Form Sasori	Complete sidequest 2 - see Deidara
Uchiha Itachi	Complete Sidequest 1 - Instead of going South in story mode to find Sai, go East to do the sidequest