The senpai knew. It happened during the water park arc, with the senpai’s prison break simultaneously happening.
I forgot who Iruma was talking to but he definitely said he was human and the senpai either overheard him, or heard it during a recording - what’s sure is that it was from Iruma himself.
Idk if the senpai shared that info tho…he was definitely salivating over that fact about Iruma but assuming a demon’s nature to keep things they like for themselves, things they desire, I’m willing to believe he didn’t share it… I’d think it was borderline yandere tbh ( ̄∇ ̄") Personally, it evoked a similar feeling to that guy smelling Kaneki’s blood in Tokyo Ghoul, a bit toned down I suppose ╮( ̄▽ ̄)╭
It was during the arc where Iruma had to relive his trauma ya know where he and forgot his name but the floating gamer guy were partnered up in a forest of some kind. He got recorded by the black teeth demon because he put a recording device on iruma right when they started. Idk if I explained it well but either way yeah it was recorded.
My only worry is the enemy finding out that Iruma is a human. Right now, more than ever, it could be a great disadvantage.
I have no doubt that his friends would come around eventually, but this needs to stay a secret for as long as possible.