Supposedly has a nice personality and is very popular as a model, though this may just be an act.

Miki was a former Evil Shinobi who joined an evil research corporation that secretly controlled the company owned by Tachibana's father, and where Yugiri's father also work.

There the evil corporation attempted to make stronger shinobi through technological enhancements. Miki (Subject 3) was the only success out of 14 test subjects. This presumably explains the horns on her head that allow her to control puppets and robots.

Since the success rate was so low, the corporation moved on to creating robot shinobi. Muramasa was their prototype. However, Tachibana's father discovers the secret lab where Muramasa was being created and set her free, giving her a false set of memories of her origin and destroying all the blueprints on how to create her.

In response, the evil corporation framed Tachibana's father for all the evil science stuff they'd been doing with his company. He professed his innocence, but even Tachibana believed he was lying.

Yugiri's father, however, did believe in Tachibana's father and begin snooping around the company. When he found out what was going on, he was going to go public, so Miki was forced to kill him and make it look like a suicide, as she had not developed her brainwashing technology yet.

She would later become a part of Senki Shu, but retained her connections to the evil corporation and often got technological supplies through them.