I forgot to put that in my OP, I'm going to add it since idk what that was about either! It all made no sense. Even if Kei hated Kou and they WERE triplets, why would Kengo hate Kou enough to slit his throat? What, did Kei conspire with Kengo and tell him about how Kou let him get raped? What, was Kengo's natural reaction to that to be willing to slit his throat? Too much missing info.
yeah that’s how I interpreted it too. But someone in the comments below brought up an interesting idea that Kou knew nothing about the rape since the beginning. And maybe it was actually kengo the doppelgänger who ignored the rape. So maybe the younger bro misunderstood all along. And if this was the case, it’d be even more twisted and messed up!

Did any of you understand the end of the 1st one (ch 4)? What was up with Kengo? I thought he was just some guy Kou was living with? It was Kei who got raped and disappeared, right? They (the rapists) were saying he's not Kou and to just pretend he's Kou. Why did Kengo slit Kou's throat? Also, Were they triplets? (/-_-)/