Ukon Tanaka operates as second-in-command of the Tsubame Group, an antagonistic faction in an alternate Meiji-era Japan opposing laws enforcing monster registration and seeking to revert monsters to their prior state. He possesses light green hair and green eyes, often projecting a self-assured demeanor and taking considerable pride in his swordsmanship skills, frequently perceiving himself as charming. His past includes training to become a master swordsman, an ambition ended by a tournament defeat that forced him to abandon his aspirations.

Within the Tsubame Group, Ukon serves directly under leader Miki Saotome, whom he consistently addresses as "princess," despite her treating him more like a servant than a valued subordinate. Hints of potential romantic feelings from Miki toward Ukon exist but remain unconfirmed. In combat, Ukon primarily engages adversaries using a samurai katana, similar to the weapon wielded by Yuko Kondo of the opposing Mobile Shinsengumi.

Ukon forms a trio with Miki and Sakon Suzuki, collectively resembling a "Terrible Trio" archetype. This group persistently antagonizes Kyoto by frequently summoning monsters and clashing with the Mobile Shinsengumi. Their coordinated efforts include assisting major threats like Yaba, though their plans often result in unintended consequences for themselves. Despite their recurring antagonism, the Tsubame Group occasionally shifts to an "Enemy Mine" dynamic, collaborating with former adversaries like Miki to defeat larger threats such as Count Montague.

Ukon’s character development remains consistent across different iterations of the series, including both the OVA and television adaptations. His narrative role emphasizes opposition to the protagonists’ goals while maintaining his established traits of swordsmanship, loyalty to Miki, and participation in the Tsubame Group’s schemes.