Make these achievements in story mode to unlock the characters:
Play as Charles The Third: complete any Story mode chapter with any two characters
Play as Dark Hero Jet Black: complete the Boss*Boss*Bang*Bang chapter
Play as Director Blue: complete the Gulliver's Battles Special Edition chapter
Play as Fighter Bianky and Friends: complete the Red Hot Rumble chapter
Play as Gran Bruce: complete any chapter with any four characters
Play as Heroine Silvia: complete the Viewtiful Cartoon World Special Edition chapter
Play as Hulk Davidson: complete any chapter with any three characters
Play as Manager Jet: complete the Atlantis: Four Adventures Of The Sea Special Edition chapter
Play as Movie Fan Joe: complete the Captain Blue Begins Special Edition chapter
Play as Rachel: complete the Les Acteurs Incroyable chapter
Play as Sprocket: complete any chapter with any character
Play as Stylish Alastor: complete the Riddle Of The Incan Empire! Special Edition chapter
Play as Young Blue Jr.: complete the Truth Of The Black Film Special Edition chapter
Play as Young Captain Blue: complete The Hidden Hideout chapter