In the credits, Kizaru's voice actor Unshou Ishizuka's name is mistranslated as Unshou Ishiduka.
The Samurai/Kimono DLC for the Straw Hat pirates are based off of the Color Spreads seen in chapters 70, 310, 373, and 526 of the manga.
The first boss in the game, Pacifista, is the only boss in the game to take visible battle damage throughout your fight. Because of this, it's possible that early in the development of Pirate Warriors, they had intended to have visible battle damage appear on bosses/characters, much like another Tecmo game, Fist of the North Star: Ken's Rage.
Completing a level as Usopp before your "Save Me, Sogeking!" special finishes will reward you with a special victory pose. Sogeking will say 1 of either 2 lines from the anime/manga, "Where is Sniper Island? It is inside your hearts...", or, "I have no reason to help you... Sogeking!" before giving his trademark pose.