It felt odd at first, but what truly triggered my theorist senses was when the new girl appeared. I was just holding myself back from posting too much spoiler details since the last chapter (self-imposed spoiler jail).
Luna's diamond pupils, Kawashina's iris seemingly flaring up when feeling bitey, new girl's snake eyes. These are details we all probably took for granted, particularly Luna's, which actually changes size. With the MC being related to Luna, there's the possibility that he too, isn't your ordinary human, should this detail lead to fantasy elements being introduced.
Chapter 4 page 3, flat teeth, possible slip-up by the author, but compare with Luna Ch.5 p.1 or drunkenillusion!Luna Ch.5 p.20.
Also compare ch.4 p.29 teeth to ch. 5 p.29/30. That's either artistic exaggeration, or her teeth gets more prominent the more she wants to bite.