Instructions
Play through the story mode of "Naruto Shippuuden: Ultimate Ninja Storm 2" until you have completed the optional side quest, Cursed Dolls. When you collect the last of the 36 Cursed Dolls, you will receive a message from the Hokage.
Go to the Hokage's office to start the Killer Bee storyline, which is a Fragment story. This means it is a short part of the game's story, unlike the larger chapters you normally play through. Watch the cut scenes until you gain control of Sasuke and the battle starts.
Fight Killer Bee with Sasuke's attacks. Killer Bee is not much of a threat during this stage of the battle, but you should play defensively so you have lots of health left over for the last stage of the fight.
Fight with long-range attacks when Killer Bee transforms into the Hachibi -- the giant ox form, similar to Naruto's Kyuubi form. Throw any fire bombs and kunai to bring his health down.
Charge your chakra until your meter is full. If Killer Bee does enough damage for you to go into awakening mode, do so. To enter awakening mode, wait until your health drops below the marker on your HP meter, then charge your chakra to activate Sasuke's Sharingan.
Use your Amaterasu Sharingan attack once you enter awakening mode. This attack deals large amounts of damage and is a medium-range attack, so you can hurt Killer Bee without being in range of his tentacles. Keep attacking Killer Bee until you fully deplete his HP meter.