The addition of secret achievements makes this challenging game to finish. Not only that, but getting the SS rank may proove to be the toughest achievement yet. Does anyone know how to unlock all the characters, costumes, and what the secret achievements are? So far there doesn't appear to be a way to find out.

http://www.gamefaqs.com/console/xbox360/code/928260.html

I unlocked everyone besides Tengu. Gonna deal with the costumes later