Instructions
Beat Neji once and Orochimaru twice to get to battle Shukaku. Watch the animated cut scene that introduces Shukaku and shows Naruto finding out that Shukaku is a transformed Gaara. Once you see "Fight Time!" appear on the screen, it's time to fight Shukaku.
Stay as close to Shukaku as possible. If you are far away from him, he will hit you with air bullets.
Hit Shukaku's head when you get the chance while staying close to him. Use Naruto's aerial move by pressing the "O" button on your controller three times fast, or press "up" on your control stick while pressing the "O" button three times fast.
Use your Demon Wind Bomb item by pressing the "X" button whenever you get a chance or when you're not jumping on Shukaku's head.
Move quickly back to get close to Shukatu's belly if he smacks you away from him. Try to duck down quickly before he uses this smack. Continue hitting his head using the aerial move until Shukaku is fully defeated. Once you have defeated him, you will have unlocked Gaara as a playable character.