there's this song i've been listening too alot lately that i really enjoy and it's got a story to it that i think would be a fun au concept.
the songs itself is "Taglio!" by S.J. Tucker, and it contains these mythological creatures called Gaselli. in their own context Gaselli are just a Gazelle Satyr/Faun variant, but Tucker ended up giving the song versions the lore of this fae called the Baobhan Sith. THOSE mfs are women with hooves and claws who dress in green and use their claws to break the skin of your neck so they can drink your blood (gaelic vampire basically)
So, the Gaselli in the song are presented as these green clad Satyr/Faun like creatures who tend animals and make bonfires at night to dance around, but they don't eat their livestalk and rather people they pick off from travaling bands by inviting them to dance and play music with them. Taglio, the character the song is named after, is an acception Gaselli who likes animal meat more than human blood, and the whole song is basically the singer going "if you get caught up with these Gaselli, you better hope the one who you're dancing with is Taglio, cause he's the only one who will let you live"
Okay! we got the song context? Now that, but make it Saiouma.
It could be a set up where Kokichi is a Gaselli who's got the same kinda lifestyle as Taglio; not interested in eating humans and prefers animal meat. but also like- it's Kokichi, so of course he'd be a little shit about keeping that fact hidden from anyone he messes with for as long as he can. Shuichi on the other hand is a human who got swept up by the Gaselli, and while to him it feels like the best luck in the world for him to have ended up being pushed around and invited to dance with the singular safe one that night, it was absolutly planned.
Kokichi saw a pretty human he really really liked, and in all his trickstery wisdom decided to fuck with the guy just so he could spend time with him and get to know him before his human band packes up and leaves their feild to travel more. What he does about that traveling bit if he gets too emotionally attached is up to y'all