Season 4, Episode 4 - "XLIII The Aku Infection"
5 November, 2003
During a fight with Aku, Jack is unintentionally infected by the sick demon. After the fight, Jack slowly becomes ill, and develops an alter-ego. The virus gradually takes over Jack's body, and he becomes more Aku-like as time passes. Eventually, the infected Jack destroys a portal in possession of some monks that would have allowed him to travel home.
