The daughter of a Yakuza boss who leads the most powerful gang in Japan. She betrayed her father when he sent her as a Vanguard to Korea by become a policewoman. She is also Ken's love interest.
In her police uniform she is usually seen wearing the uniform cap and shirt but a revealing miniskirt. Despite the restrictions, she wears heels. On her back she has a special dragon tattoo that only appears when her body temperature rises. Her father made her get this tattoo to offiicially make her part of the gang. She also wears special dragon earrings.
Yumin hates gangs and her father because her mother and sister were killed by gangsters. For the most part she is cheerful towards others. She has feelings for Ken.
Ken sees Yumin and falls in love with her. He confesses his love to her but she turns him down saying that she can't go out with him because she is Korean and will soon be moving back to Korea. She then tells him that she will become a policewoman.
When Ken comes to Korea they meet again and in his nervousness to make a good immpression he tells her that he has been working as a video game developer in a gaming company. She visits his "office" and wholeheartely appears to believe him despite the fact that a group of men had been contradicting everything that Ken said in the cafe they had been eating in earlier.
When Ken comes back from his training he meets her again while out walking, she appears to be fairly distressed but asks him out to dinner. After dinner they are out walking when her bag is grabbed by some men on a motorcycle. Ken dashes to get the bad and attacks one of them men with his shoe. Yumin shows off her skills by bounding after them, beating them up and getting her bag back.