The son of the Emperor, and thus a prince. After being sent to the future by Aku, he adopted the name "Jack" because the locals kept calling him that. His birth name has never been revealed. He spends his days fighting Aku and various villains with his Sacred Sword. He is serious, polite, and stoic, though his occasional naivety allows Aku to trick him. He is characterized by his signature white gi. His goal is to find a time portal scattered somewhere in the world to return to the past and destroy Aku. He appears to be in his 20s. He can never ignore those suffering under Aku's tyranny. While highly intelligent, he is often baffled by the advanced technology of the future.

The Shapeshifting Master of Darkness. Jack's nemesis and rival. While he is the incarnation of evil, he isn't purely malevolent; he shares a complex love-hate relationship with Jack and often displays petty or cowardly behavior. He frequently shows a surprisingly human side through these pathetic and comedic moments. His comedic chemistry with Jack is a highlight of their encounters. In terms of power, he has no equal except for Jack; however, against Jack wielding the Sacred Sword, he is often helpless. Their encounters usually follow a pattern: they meet, they fight, Aku loses, and then Aku flees. He resides in a dark, crimson lair.