#And Sullivan is too overcome with grandfatherly-bliss to notice

[cactuskat]

Demon Swap: Sebastian from "Black Butler" and Lord Sullivan from "Welcome to Demon School Iruma-Kun!"

Imagine if you will, a Ciel who makes his deal with Lord Sullivan, but Sullivan does not require a soul, instead requesting that Ciel become his grandson. This has to be the easiest deal a human has ever struck with a demon, but oh, how mistaken that was.

Ponder perhaps, an Iruma who's soul is sold by his parents to the starving demon Sebastian, only for Sebastian to find, he'd like instead to refine this soul before devouring it, afterall he is a demon a finer tastes, and thus the Butler persona is born.

Ciel returns home with an... estranged relative(?) eager to take Gaurdianship over the newly orphaned earl

Iruma is taken to the demon realm, suddenly placed upon the lap of luxury, with a loyal butler pleased to do whatever he says- only Iruma has no clue what he even wants

Is Ciel safe- Oh yes, definitely, Lord Sullivan is formitable force when he wants to be, and he will tear apart anyone who dares attempt to hurt his grandbaby, and what's more is more than willing to do anything he asks as per their agreement. But oh, oh how Ciel often replays the events of that terrible day, and wishes he perhaps negotiated for different terms for their contract...

Ciel, tries to solve a murder, as Sullivan Fawns in the background ("Oh my goodness look how cute my grandson is!!! He's doing such a good job, don't you think Opera?? I should find him a little detective's outfit, he'd be just precious!!!!!" "NO!")

Iruma meanwhile is far too aware of the fact that he's just glorified wagyu, but you know what? This might as well be how his miserable life ends, he could enjoy it... he supposes... just has to learn how to enjoy things. Thankfully Sebastian is one hell of a butler and knows just what Iruma wants right when he needs it

and of course he helps out behind the scenes at every chance he gets, he's not going to let his snack be discovered by the rest of demon kind afterall. Sometimes not even behind the scenes, school rules be damned, any butler worth his salt goes wherever his master does. Professor Kalego hates him