This game has been released in Japand and this is how you unlock the characters in that game. If they do not change it when it comes to America, then these will be alot of help.

Play as Gogandantess
Successfully complete story mode with all twelve default characters, then defeat Gogandantess in versus mode to unlock him.

Play as Jujudormah Ran
Successfully complete story mode twice with Jujudormah, then defeat Jujudormah Ran in versus mode to unlock him.

Play as Kojirou Sasaki
Successfully complete story mode with Miyamoto Musashi, then defeat Kojirou Sasaki in versus mode to unlock him.

Play as Mega Man EXE
Successfully complete story mode with Samanosuke Akechi in story mode, then defeat Megaman EXE in versus mode to unlock him.

Play as Miyamoto Musashi
Successfully complete story mode with the small fish soldier, then defeat Miyamoto Musashi in versus mode to unlock him.

Play as Nobunaga Oda
Successfully complete story mode with all twelve default characters, then defeat Nobunaga Oda in versus mode to unlock him.

Play as Zero
Collect the Green, Blue, and Purple Crystals with Mega Man EXE to unlock Zero.