Jack helps save a Prince and Princess whose ship has been shot down to Earth by Aku.
EP 12 XXXVIII
When ancient gods try to destroy a powerful evil, they send one piece of the beast hurtling through space. This piece lands on earth, spreading its evil through the land. When it encroaches on an Emperor's empire, he takes it upon himself to destroy the evil, but ends up unleashing the evil that is Aku.