Saw a spoiler before saying that he didn't travel to the past like Lippe but he has dreams about the original story line. And he liked Lippe even in Lippe's first life and he something like proposed to Lippe to help her family but Lippe rejected him.
Is it me or did Lippie and Castellio had something going on in the past? Also I find him suspicious, is it possible that he also traveled back?