????

basically, if Kouichi "consumes"/takes in anything originally from that other world (the one he was summoned/forced into), he has to stay in it (cuz it anchors him to it). That "anything" being Caius's blood or cum (aka Caius would have to ejaculate inside Kouichi or feed him his blood); so in order to give Kouichi that final choice - to stay or return to his world - Caius never gave him any of that.

Thanks love