Oto Tachibana

She's the sister to Mikazuchi and love interest of Yamato. She was sent as an undercover agent to win Yamato's trust and steal Susanoo away from Yamato and murder him. Things become complicated as Oto develops a real bond with the group and even falls for Yamato. Because she has been contaminated, she was also marked for death amongst her peers. She later finds out that she's actually not related to Mikazuchi, but a little girl taken away from her real mother. Mikazuchi however never knew about this and after being possessed by Orochi he used the dark energies of Orochi to corrupt Oto's soul. It was not until Orochi broken the psionic bind between Mikazuchi and his mech that her mind was free from dark influence. Towards the end of the series she now lives in the village along with Yamato. There was no epilogue to speak of her fate, but it is assumed that she will eventually have a real romantic relationship with Yamato and marry him.

Source: Wikipedia