King Yukio was the ruler of the Land of the Coliseum. He sits in the royal box, behind bulletproof glass, during Kino's participation in the tournament.

Seven years before Kino's visit, the current king, King Yukio murdered his father by poisoning him. To cover up this deed, he murdered the doctor presiding over the late king, and replaced all the ministers and courtiers.

A bloodthisty monarch, King Yukio also set out to eliminate his own family to prevent an uprising via execution or exile. His wife killed herself from the grief, and their only son vanished, his fate unknown to the countrymen.

He began to run the country with arbitrary laws, and implemented the tournament when citizens began to flee the country - declaring that only those proven most worthy may become citizens.

Yukio's son Shizu returns seven years later to participate in the tournament in hopes to kill his father.

He is killed by Kino when she shoots a bullet at him with the mock intention to kill Shizu.