U-ko is a ghost from the Obake world who came to the human world out of admiration and now resides there with the Koizumi family, specifically Yoshiko Koizumi. She maintains a romantic relationship with Q-Taro, though her temperamental nature frequently sparks conflict between them. Tomboyish and an active judo practitioner, U-ko often uses Q-Taro as her practice partner during their encounters. She exhibits violent outbursts and poor housekeeping skills, and is also a terrible singer. When she sees Q-Taro, she sometimes delegates chores to him. U-ko admires the intelligence of Doronpa, an American ghost; this admiration fuels Q-Taro's rivalry with Doronpa and causes friction in her relationship with Q-Taro.