Naruto

Sakura shuriken combo:
Push A, A, A buttons.

Haku combo:
Push A, A buttons.

Sasuke's combo
Push B, B, B, B, A to perform Sasuke best combo.

Unlock Attack Power 4:
Win 1st place in the Time Attack mode.

Unlock Difficulty 4:
Win 1st place in the Survival mode.

Unlock Kyubi Naruto:
You have to unlock Rock Lee first. Now go to one player, not story mode. Now
have fun with this part, you have to beat one player mode with everyone, twice!
Once you do you'll get a message that goes something like this, Press X or Z while
highlighting Naruto to play as Kyubi Naruto. He's VERY fun to play as.
Note: He doesn't have a Kunai, instead when you use the A button he uses his
claws to attack. His special does almost as much damage as Kakashi's fully
charged special. Submitted by: Kyubi Link

Unlock Sharigan Kakashi
Unlock Kyuubi Naruto, then finish Single Player mode with him.
Then, finish the Single Player mode with Kakashi. Go to the character
selection screen, highlight Kakashi and press X or Z.

Change clothes:
Highlight a character and hit Y

Unlock Rock Lee
Beat Zaibuzan without using a single continues in story mode.
After, beat Rock Lee when he appears.

Haku without mask
Finish the arcade mode with Zabusa on difficulty 3. Push X or Z buttons
while highlight Haku at the character selection screen. You can play with
him without mask.

Unlock Sound Test in the Omake menu:
Finish the entire game at least once with all original characters in
single player mode