Making the executive decision to call this au Teifling Iruma au, or just Teifling au.
((Insane ramblings (reasoning) under the cut))
Iruma is still a normal human in this au, he just kinda obtains demon traits, so demon or half-demon don't technically fit.
Teiflings are humans that whoopsies got demon traits whether from bloodline or (more importantly) curse/magic.
According to the dnd wiki;
Tieflings are created in one of three ways: as a human transformed into a tiefling using powerful magic; as the offspring of an existing tiefling; or as the offspring of a human and a cambion or half-fiend. [source]
Idk about you but 'human transformed into [demon] via magic' sounds pretty damn close to what we're looking for; Iruma being fully human but gaining demon traits through magical means.
Shoutout to this comment by @nerdy-girl-named-pumpkin btw, I didn't know this before you said it and I'm absolutely using it
Which tbh reenforces why I'm calling it teifling au. Human+magic=demon traits=teifling. :))
If anyone else can think of a better name that like. uses an actual mythological creature instead of just me being a dnd nerd. Let me know, I'm totally down to learn stuff like this but don't feel like going down a mostly-aimless Google rabbit hole.
Iruma woke up with a stretch and a yawn. He had a minor headache too, but he wasn't too worried and he just ignored it. He got out of bed and started changing into his school uniform.
There was a knock on his door, which was most likely Opera. Sullivan tended to just barge in, but at least Iruma could usually hear him coming. The monotone voice coming from behind the door confirmed Iruma's guess. “Iruma, are you awake?”
“Yeah, I'm up,” Iruma responded, pulling on his jacket and opening the door. “Good morning, Opera.”
Opera nodded, pleased. “Good morning, Iruma. I'm going to start making breakfast. I wanted to check on you before I did.”
“Okay. I'll go finish getting ready then.” With a nod, the two went their separate ways. Iruma made his way to the bathroom to freshen up before getting breakfast. He applied his special perfume and brushed his teeth before starting to brush his hair.
Iruma's fluffy hair naturally led to an extra frizzy bedhead, so he tended to deal with it last. He combed through his bangs first, that way he could actually see what he was doing. While he was brushing the rest of his hair, his comb got stuck. Knots in his hair weren't uncommon, but after trying at it a few times it didn't budge. This felt a little different too, which was weird. Confused, he tried going through his hair with his fingers when he found what his comb got stuck on. It wasn't his hair that his comb got caught on, apparently. Wait. He checked the mirror to get a better look. What?
“I'm… growing horns?”
Iruma stood there in shock. He stared at the little black horns just beginning to sprout from his head, sitting a few inches above his ears.
. . . . . .
“I’M GROWING HORNS!!”
Iruma's eyes shone as the shock wore off, the situation fully hitting him. He has horns! He bounced in excitement before dashing towards the dining room. Iruma didn't bother to finish brushing his hair, he'd do it later. He wanted to show his family his new horns! “Grandpa! Opera! Look!”
——————
Opera was serving Sullivan his tea, having just finished making breakfast. Iruma suddenly came rushing into the room, his hair still mostly unbrushed and eyes sparkling. “Iruma-”
“Grandpa! Opera! Look, look!” Iruma said excitedly, cutting Opera off. He shifted his still-unbrushed hair out of the way, catching the two demons off guard. “I'm growing horns!”
True to his word, Iruma now had a pair of small black horns on his head. Opera hadn't noticed them before, not even when they'd checked on the boy earlier this morning. They probably hadn't noticed because the tiny horns had previously been hidden beneath Iruma’s disastrously fluffy bedhead. But how did they get there in the first place? Iruma was a human, and humans didn't have horns.
Opera didn't have time to dwell on that thought though, since Sullivan had just pulled the boy in question into a hug. The two of them were laughing, both absolutely beaming. Opera had never seen Iruma with a smile quite as bright as the one he had now. Sullivan never looked more proud as he held up his grandson, praising his new horns. Giving a small smile themselves, Opera snapped a picture of the two. This was a moment they were sure all three of them wanted to remember.
Opera let the two have their moment before speaking up. “Iruma should finish brushing his hair. He can talk more about his new horns during breakfast.”
Sullivan pouted, not wanting to let go of Iruma. Opera was about to convince him, but Iruma spoke up first.
“Oh, right! I'll do that and be right back,” he said, having seemingly forgotten about brushing his hair in the excitement. He gently released himself from Sullivan's grip and made his way back to the bathroom. Opera fought with Sullivan to keep him from leaving the room, reasoning that Iruma would be back in only a couple of minutes.
