I figured that Midou would wreck her ... now she is Midou's bitch LOL. Whatever Midou did to her was so bad that she now has PTSD.
Mama always used to say don't stick your dick in crazy but in this case Sister-chan stuck her nose (and mouth/tongue?) in crazy. Who is the side character again? Well, surprisingly I don't feel bad for her. I feel bad that she is the next victim but at the same time your mouth shouldn't write checks that your ass can't cash.
Also, this basically confirms that Midou did not lose her memories. It was all faked out. A psychopath on this level would be able to do that easily.