A strong-willed and stubborn schoolmate of Kai, Mao, the daughter of the head of the Jahana Yakuza, is often bossy and likes to be in control, a trait she probably picked up from her father. Her blunt, confrontational demeanor seems to be a brave facade she puts up whenever things don't go her way or she's scared.
After Mao meets Okamura and realizes he knows something about Kai's disappearance, she forces him to take her along by financing the trip with money she steals from her father, implying he would try to kill Okamura for the theft.
She is determined to stick by Kai's side, despite his best efforts to shield her from the danger surrounding him and Saya. As the series progresses and she comes to terms with Kai not returning her feelings, Mao warms up to Saya. The only girls "in a group of men," she grows more protective and concerned about Saya's well-being as Saya's health seems to decline.
When she accidentally overhears Saya and Hagi's conversation about Saya's impending thirty year hibernation cycle, Mao becomes furious and slaps her. She agrees to keep it a secret from the others, then tells Saya she will make a promise with her, a promise between two women, to personally bring Saya back to Okinawa once everything is over.
Mao finally decides to test Kai's feelings once and for all and kisses him, but he doesn't respond and seems baffled by her actions. Realizing her love will never be returned, she gives up and begins to play matchmaker between Kai and Saya.
She later accompanies Okamura to the the Middle East.