[Qikz]

Spoiler for Episode 7:

I don't think it's so much an Evil Tenshi, more of an agressive Tenshi. Maybe Tenshi realised she wouldn't be able to stay with just defensive skills, so she created the Harmonizer thing to allow her to split in two, Agressive and Defensive to be used in certain situations?

When it splits off from her she does it to help them, so either something malfunctioned or she hasn't used it before so doesn't know how to keep it under control.

Thing that makes me think this, is she claims she has to help them/save them, but she can't do that in Defensive form.