Utao is the younger sister of Kyohei and the current partner of Kukuri. She comes to Tokyo to meet her brother out of fear that Aki would come for him. Her fears are confirmed and after destroying Kyohei's apartment while confronting Aki, she moves to Hibino's house with her brother, working at the Shiba family's cafe while training herself to improve her control over Kukuri's movements. She seems to have a brother complex towards Kyohei to the point of getting angry on any other girl who approaches him.
Source from Wikipeida