The shock of seeing the direct result what she had just caused was what finally broke Mumei's brainwashing.

She'd been doing it for years, but without the Kotetsujo crew, she never would have even questioned it.

Quote Originally Posted by shinta|hikari View Post
Horobi type characters make no sense to me. Why would you go so far for someone who clearly doesn't give a shit about you? It's different if you're like Mumei, being fooled in one form or another, but Horobi knew she was trash to him and yet still killed herself for his revenge.
That is actually what made this episode not just good, but great. It explains what complete scumbag Biba has become for his own personal gain. This is obviously a fight he started with the shogun, and perpetuates by being a incredibly evil POS.

There is one key thing to notice is the composition of Biba's forces. All the regular warriors (and scientist) are male, and all of Biba's manufactured Kabaneri have been female. He charms and brainwashes girls from a young age to be loyal to him, worship him, maybe even love him. Horobi, by far the oldest Kabaneri we've seen Biba have, is still fairly young. We can presume he started with her.

Then he injects Horobi and her wonderful ass with the blue blood, turning her into a black cloud hybrid. She eventually loses control, and starts slaughtering their own forces, and stops right before killing Biba. She hesitates because he's formed the cult of personality around him, Horobi was still ultimately loyal to his greatness, and he kills her, face completely calm.

But that's not entirety of that scene. That's what his people see, but something else plays between Horobi and Biba. That single, perfectly animated bead of sweat. Brilliance in visual storytelling right there. Biba was scared. He assumes his female Kabaneri still love and are loyal to him, but he's not completely sure. Horobi, regaining control of herself in those final moments, notices that little drop. A knowing smirk plants itself on her face before she lets him kill her. He keeps it off his face, but she saw his weakness.

He could use men as Kabaneri, but they wouldn't worship/love him the way his brainwashed girls do. He'd lack that final safety net.

One he just lost with Mumei (thanks to the Kotetsujo's crew casual humanizing and deprogramming) and that he probably doesn't even realize (except that dumbass was speaking her final lines this episode out loud, so maybe, maybe not).