Maya Ooba
One of the main female characters. She is known as “Black Maya” from her ninja clan. She is a runaway ninja (reasons are unknown), but still acknowledges herself as a ninja from her clan and upholds the traditions of her clan. One of the traditions is to keep their identity secret, or else they must kill the one that knows their identity. Kazuya found out about her identity when he came across her ninja tools. As she commenced combat with the Hina as a Guardian Heart protecting Kazuya from Maya, Kazuya helped Maya escaped. Thus she owes him, and as one of the traditions, she must pay the favor back—and so she ends up living together with him. She hates Kazuya in the beginning, especially when she had no choice but to become his wife because he saw her naked twice (as well as being kissed twice by him) which is one of the ninja traditions. However throughout the show, she later warmed up to him when she realizes he is reliable and kind, she constantly thinks that Kazuya is fated to be her husband, and in the end she accepted Kazuya to be her husband but still cannot express her feelings well. She hates the guardian heart as well for beating her in a fight.
In episode 2 of Guardian Hearts-Power UP! she confessed that she is in love with Kazuya.
In Episode 4 of Guardian Hearts-Power UP!, there is a short clip after the credits showing Maya giving her Christmas present to Kazuya and telling him that it doesn’t matter who he loves, as long as she is allowed to keep her love for him. After that, she kissed Kazuya & told him that she won’t give up on him (which was overheard by Hina and the others).