Imagine after this arc, it's revealed that Seira is the Sanest girl so far, and as much as how the story presents it Seira doesn't seem like the girl who would go that far especially towards Masato, unless Masato fumbles every dialogue choices after this
Looking back, Seira is statistically unlucky within her friend group. All of her friends have boyfriends and yet none of them mentioned that they were sharing their respective boyfriend with another girl. Seira was the only one unlucky enough to find a guy who was already dating another girl.
Something tells me that one of them is watching, Gods it'll be one hell of a left hook if they reacted like a cuck. I highly doubt that'll be the case but the pacing and the direction of the story just surprised me compared to other Romcoms
If Kouta exhibit a passive aura that NTRs and makes the girls fall in love with him
Then Purple devil exhibits the aura that makes every single person around her dumb as rocks including her little sister