The majority of characters can be unlock by playing the story mode where you are going to get Storm Points (SP). The ones that requires extra SP are the next ones:
Killer Bee - 540K SP
Sasuke Uchiha ("Taka") - 560K SP
Lars (From Tekken) - 600K SP
Fourth Hokage - 580K SP
Another way to get this trophy is while you try to get the title that requires to use 30 times a character, that’s going to give you a lot of SP.
For one reason Hokage Naruto is not require for this trophy, something that is necessary to have in the PS3 version of the game.