She is the sacrifice of the female Zero pair. Unlike Kouya's solemn demeanor, Yamato has an outgoing and lively personality. Their relationship is highlighted in a mini-arc within volume 4.
The bond between Yamato and Kouya is intense and devoted, but it becomes unexpectedly stressful for Yamato in volume 4. Her marking, which she views as tangible evidence of her connection with Kouya, begins to fade without warning. Both girls have the same marking—a zero with a line through the middle—located on their breasts, making a clear reference to the homosexual nature of their relationship.
(Source: Wikipedia)










