Okay, I get it.
Anon met Koishi on the surface, became fond of her in a platonic way, followed her to the Underground, met the rest of the Komeiji family, Satori became fond of him, so Koishi became jealous and manipulated him so that he raped (or just molested, I'm not sure) Satori and then attacked her in retaliation, filling him with guilt because it was "just his unconscious desire".

Still unexplained for now is how Koishi changed from "I trust him, he's not that kind of guy" to "you are a horrible person, that's what the result says". If it was jealousy, her hostility would've been focused at Satori. Unless she planned from the beginning to fill him with guilt to make him her pet.

Jealousy is a terrible thing.

It could be that she does trust him to act as a gentleman, which is why she manipulated his subconscious to act like a beast, thereby tying him to her out of a sense of shame and guilt. It could be that she targeted him because she's unable to manipulate Satori's subconscious, just as she cannot read Koishi's mind. But who knows? My Japanese is broken at best and infantile at worst, so I can't really follow the dialogue.

To be quite honest, I'm on pins and needles right now. I'm doing my best to help get this thing translated properly, and given Koishi's actions of late (i.e. manipulating this man who she seems to genuinely care for into raping her sister, then beating her till she can barely stand.) And now, she defends him? I'm just at a loss at what to believe, what is Koishi really feeling? Those eyes hide some deep, dark secrets, gentlemen.