At first I also thought like that... But there is still something strange, it seems that he knows that Rose is not the real Rose, and he also has a different interest in Rose where he even helps Rose find a book that is difficult to obtain through a shortcut by introducing Rose to his real family, but what is interesting about Rose and Erin is they both have something in common, that is, they are both too honest so there is nowhere they cover up the hidden intentions of what they are doing... That's what keeps me curious and keeps me reading this story.hehe
I'm lazy so I'll just copypaste an old reply of mine about the same topic:
That, or a demon or something. Part of my suspicions/thoughts for this is 1) how he controlled Mila into giving Rose the map to the Crimson bookstore place 2) how in one of the books he showed Rose at the bookstore, one was for summoning demons. Plus, this is another one of those tropes as well.
Either way, def giving nonhuman vibes.
Tbh my thoughts haven't really changed from then, it could be that the demon things are just red herrings or it could be just as well related to something holy.
Seeing how in the most recent chapter (39) we got to know about the three supreme beings in this world - God, The Spirit King, and Dragon(s?) - and seeing how much it seemed to focus on dragons, him being a Dragon wouldn't be surprising I guess? It does make me think then, it would make sense that he's here for entertainment but how is it that a dragon is also the most dangerous thing to Calix/ML rn? Is it him, or a different dragon? What about Rose and her diary? Still v much intrigued by that.
Honestly, I still haven't found any interest in this story, but I will continue reading this story until I find out who Erin really is, whether he is indeed a human or a high-class mage, and why he works in the same place as Rose... Of all the characters, it is only that man who really makes me curious, the rest I haven't found any click in my heart... This is just my personal opinion.