Fight as Evil Rugal B
Hold Start when choosing Rugal B. at the character selection screen.

Alternate endings
Successfully complete the game with the following characters on your team to view a different ending:

Andy, Benimaru, Robert
Billy, Chang, Joe
Chang, Chin, Choi
Chizuru, Iori, Kyo
Chris, Kensou, Shingo
Chris, Kyo, Saisyu
Chris, Yamazaki, Yashiro
Clark, Lucky, Terry
Goro, Joe, Yuri
Heidern, Leona, Ralf
Iori, Kyo, Shingo
Kim, Saisyu, Takuma
Kyo, Ryo, Terry
Kyo, Saisyu, Shingo
Mature, Rugal, Vice
Mature, Shermie, Vice
Ryo, Takuma, Yuri