Viletta = a bitch that grew up getting shit on, worked her ass off to stop being shat on, got screwed over anyway, and just can't fucking catch a break. The only things in her head are anger, hate, and despair.
Chigusa = Viletta if she never had to go through that shit. Naive, pleasant and helpful. Not to mention the first person she met after losing those shit memories was a nice Eleven man who took her in, cared about her, had a nice relationship, and fucked like a tiger. She found peace in happiness in the little things, despite not having power. Because in Chigusa little world, there wasn't any Britannian shit about the strong abusing the weak.
Until those Elevens tried to kill her, and suddenly that made her remember all the shit she grew up with all at once, turning her once again into a cold-hearted bitch. Except now she still has memories of the time with Ougi, so in addition to the anger, hate, and despair, there's a small shred of happiness and love. Of course, she can't just throw the negative feelings away and be with him, but she'll probably wind up in the Black Knights one way or another.