Yuki

Yuki was originally a shinobi with a different name at a Good Shinobi school. However, she was often belittled and looked down on by her fellow shinobi, and thought of as the small fry of the team.

One day, she and her team were sent out on a mission. Yuki scouted ahead and encountered a Yōma. Her group was not high enough rank to know about Yōma, so she thought it was some sort of monster or demon.

When Yuki came back to her team to report the monster, they didn't believe her and ridiculed her for believing in monsters. However, soon the Yōma attacked the group and only Yuki was able to get away.

Yuki's school refused to officially acknowledge the existence of Yōma, and so the "official" story of the mission became that Yuki had turned traitor and killed all four of her teammates.

Disgraced and cast out, Yuki was found by Reki who recruited her into Senki Shu and gave her the name Yuki. Afterwards, Senki Shu erased Yuki's original history.

However, while records could be erased, that couldn't stop people from talking. This would lead to Kochō eventually finding out that Yuki's past as a good shinobi that betrayed and murdered her team. However, she soon hears the true story from Yuki herself.

While Kochō and her allies sympathized with Yuki's backstory, they could not ignore the evil actions she had taken with Senki Shu and still had to stop her. In response, Yuki consumes an experimental drug she got from Reki and becomes strong enough to take them all on.