The best and safest method is directly from the on your PS Vita:

Omega Force perfected their "Warriors" formula with this sequel. Unlike the first game, which stuck strictly to the anime’s timeline, dives into a unique "Dream Story" arc. This means even the most hardcore manga readers get a fresh narrative featuring the New World crew.

The game follows the "Musou" formula where players clear waves of enemies to capture bases.

Let's be realistic. The Vita version is an admirable port, but the PS3 is simply a more powerful machine. You can find direct comparisons online showing that the Vita version often has reduced draw distances and lower-quality textures on backgrounds and enemies. One review aptly described it as a faithful copy, but "technically inferior" to its PS3 big brother.