Rapid-Fire Older Brothers Headcanons
Mammon and Leviathan have an ongoing bet regarding which one of them has given Lucifer the most grey hairs. Neither of them dare to actually ask Lucifer, though, so it's mostly hypothetical.
Lucifer, as we all know, likes classical music. Sometimes, Levi will try to see how many classical or orchestral versions of random meme songs or game tracks he can play in a row before Lucifer notices what they're listening to. How long he can keep the bit going for varies wildly depending on how familiar Lucifer is with the original songs, but generally, he gets at least a solid five minutes of Lucifer, completely oblivious, listening to the wildest stuff. Mammon usually ends up filming this. A gif they made of Lucifer dancing along to Rush E has become a reaction image in every single group chat he isn't in.
Leviathan will ALSO often play those "[song] but terrible" or "[song] but I got distracted" videos to see how long it takes Lucifer to notice. Those ones tend to get noticed far quicker, though.
Mammon is really into found object art and scavenging for craft supplies. Somewhere, in a desk drawer, Lucifer has a necklace made out of can pull tabs and pretty rocks that he looks at whenever he's mad. Leviathan's favourite coaster is made out of bottlecaps with words and flowers and game logos painted on them. Most of the "mess" in Mammon's room is actually just stuff he hasn't gotten around to actually making into art yet.
Lucifer, Mammon, and Leviathan have a Minecraft server. It wasm originally just Levi trying to suggest a way for Lucifer to destress, but now it's just them goofing off. Levi built a squid cannon outside of Mammon's base. Lucifer will regularly leave signs in Levi's base, reminding him to drink water and eat something if he's been online for too long. Mammon once lured the Warden all the way to Lucifer's base, named it "Stess," and just... Logged out. Lucifer still hasn't forgiven him.
Sometimes, Leviathan will just walk into Mammon's room, throw something at him, and run for his life. Mammon always catches him. This is always completely unprompted, and nobody knows why he does this. It's just funny to him.
Lucifer has a habit of just staring at people, silently, with no discernible expression. His brothers tend to assume that this means he's angry at them. In reality, it's just because his brain is stuck in a loop of "Baby. Little brother. Tiny. Precious. Little tiny baby. Fragile. Baby. Small." He can't help it. Sometimes, he just randomly remembers how young and fragile his brothers are in comparison to him, and just... Short-circuits. Just full-on bluescreens. He also occasionally does this with Cerberus, but - due to Cerberus being a dog - he'll typically just start actually baby-talking the Goodest Three-Headed Boy. Mammon has caught him doing this a few times.
Levi and Mammon both journal to help them organize their thoughts. Levi's journal is more like a mix of a scrapbook and a diary, full of polaroid photographs and long, poetic accounts of his experiences and emotions. Mammon's journal is more practical, mostly being used to keep track of upcoming events, important things that happened that day, to-do lists, and notes from class or meetings.
Mammon keeps a list of every single person who Leviathan is mad at, and actively refuses to do business with any of them.
Lucifer can drink an entire pot of coffee in less than five minutes. And often does.
Levi & Mammon used to show up to Lucifer's room in the middle of the night back in the Celestial Realm whenever they had nightmares, and bully him into tucking them in and singing them lullabies until they were ready to go back to sleep. They don't do that anymore because they consider themselves too grown up, but there have been a few times that they've seriously considered it. Levi occasionally goes as far as Lucifer's door before changing his mind. If he didn't change his mind, Lucifer would still gladly sing him to sleep - because no matter how big they get, they're still his baby brothers, and he still loves them dearly. But he'd also absolutely hold it over his head for weeks.
Mammon's immune system is near Olympian, and Lucifer's is pretty damn good, too. Leviathan, however, gets sick every single time that someone so much as breathes in his general direction wrong. Whether this is why he never leaves his room or because he never leaves his room is up to interpretation.
One time, one of Mammon's crows got hurt - and for literal months, the entire house was flooded with them while the little guy recovered. There were at least a hundred. They were everywhere. Thanks to this, they're now very familiar with the rest of brothers, too - and can occasionally be found following them around.
Leviathan doesn't just sew his own cosplays - he also sews the vast majority of his clothes. He's also usually the person who fixes the rest of the family's clothes whenever they get damaged, since only him and Asmo have any sewing knowledge whatsoever. One time, Levi made matching plushies for the twins on their birthday.
