Back when Yang was still a jerk, Yang promised Coop that if he did him some favors, he would get Yin to go on a date with Coop. When Coop comes to go on the date, Yin makes it clear that she won't go on the date until Coop starts acting evil again. Master Yo discovers Coop's aura is split into half-good and half-bad, and the bad aura needs to be taken away. The only way to do that is with a magical set of suspenders and a bow-tie. Master Yo goes on a quest to retrieve the magical items and instructs Yin to go on the date to make sure Coop doesn't become evil. Yang goes on the date, too to antagonize his sister, making her mad. When she gets mad, it makes Coop mad, and he turns evil. His evil spreads to Yin, making her want to be with the evil Coop even more. Yin is uneasy with hurting people and tries to stop hanging out with Coop, but he makes her even more evil, and they go on a rampage. Yang tries to prevent Yin and Coop from getting into the Night Master's lair until Master Yo can return with the magical items. Yang has to battle with three incarnations of evil Yin.