You can call me Celeste, and I'm not much of a writer, but I get a lot of enjoyment from writing things for myself (particularly reader insert content, both romantic and platonic), so I thought I'd try and share them here on Tumblr!
All fics will feature a gender neutral reader unless stated otherwise!
I've always liked the idea that each and every individual human has a dominant sin, and that demons of that respective sin are better equipped to tempt those souls due to that connection.
This also goes along with my headcanon that every demon is assigned into one of seven categories from birth, colloquially known as the Seven Deadly Sins. It's a natural and instinctual part of their existence, where they can sense the sins of humans and prey upon their lack of knowledge and ignorance.
It would, of course, be especially prevalent with the Brothers, as they were assigned as the Avatars of these sins by the Demon King.
Most lower level demons have the baseline magical compulsion to prey on humans with a compatible sin, but that doesn't say anything about their skills in magic and manipulation. They likely run on base instinct alone unless they are supremely passionate about their education at RAD XDDD
The Brothers, on the other hand, are naturally very powerful and, whether some actually appear this way or not, are also very intelligent (at least when it comes to their sins!)
Basically, you can't underestimate any of them, because if they really want something, they'll do whatever it takes to get it.
As an example, I view my MC's main sin to be Pride, and she just so happens to bump heads with Lucifer on many an occasion, precisely because of their similarities! And just as much as he can understand her on a fundamental level and use that to his advantage, my MC is smart enough to be able to do the very same back to him!
I mean, any human arguably could as well, but I'd imagine Lilith's genes definitely help my and many others' MCs out a great deal in those cases too XDDD
They're both too stupidly prideful for their own good, trying to one-up eachother like a couple of kids. It's almost like a feedback loop; where my MC attempts to get Lucifer to childishly rise to a challenge by using his pride to her advantage, but even when she succeeds, Lucifer can still relish in the feelings of her own pride at succeeding!
I feel like there would be some sort of spell or magical item that can allow a human to get an almost mathematical breakdown of their sins, kind of like a pie chart or some other type of visual, which I imagine would be beneficial knowledge for any sorcerer or witch preparing to interact with demons to any extent.
I believe that any human is susceptible to any demon's temptations, but there are certain combinations that allow for a higher success rate than others.
As another example, my MC's second most prominent sin would likely be Sloth, and so she has received one too many solicitations for naps from Belphie, who can sense exactly when would be the best time to ambush the idea onto her XDDD
I also like the idea that when a Demon makes a pact with a Human, their ability to sense that Human's sins is significantly heightened. (I'm hoping to write about this particular element in more detail for the brothers sometime soon 🤞)
Where in a non-pact situation, a Demon may only sense a sin if a Human is really struggling with it at that current point in time - in a situation where a pact is formed, both parties have agreed to open a magical bond where in exchange for the Human having power over the Demon with commands, the Demon can more freely take power from them without necessarily obtaining their soul.
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Since I've not had much time to work on my character specific headcanons, I figured I'd post a more rough-around-the-edges sort of post where I don't really have to proofread and can just infodump for fun XDDD
✦ To be honest, Levi pretty much forgot that the Human Exchange Student was going to be arriving that day. I mean, he had so many more important things to worry about, so what reason would he have to care about a simple human?
✦ …Actually… He could use this to his advantage. Would it be petty? Maybe, but it would serve Mammon right for being such a scummy brother!
✦ And surprisingly enough, his plan worked! But despite what his brothers were insinuating, he didn't care for you in any way! Not at all! Not one bit!
✦ It's not like he was practically living within one of his favourite anime tropes, having become the unsuspecting onlooker to a real life isekai! An innocent human suddenly thrust into a world of magic and demons! An instantly compelling setup that had made him fall in love with many a main characters…
✦ But regardless of any of that!!! He was just a stinky Otaku who gamed his days away in the comfort of his room. There was no need for him to get involved with whatever daredevil antics the human and his scummy brother were bound to get up to.
✦ …That wasn't going to be as easy as he wanted, however.
✦ Because this human just didn't know when to quit! I mean, why do they get to have so much fun binging TSL and then act so confident as if they know what they're talking about? It just wasn't fair.
✦ And now here he was, standing in front of a terrifyingly large crowd in the main hall of RAD, just to prove to one singular prideful human that he was the ultimate TSL fan!
✦ …He really didn't want to hurt them. He honestly felt downright awful after his outburst. But most of all, he felt defeated.
✦ Did he believe that you cheated during the TSL Showdown? …Kind of, yeah. Actually, yeah, he did think it was a scummy thing to do!
✦ But… it's not like he was in a position to have the rarest of merch or all the insider details of his favourite story. And that's simply because he was a shut-in. He keeps to himself and he never tries to interact with others.
✦ Whether he likes it or not, you got the advantages and opportunities you had because you actually interacted with people and made your own impression on them.
✦ And that made him so jealous.
✦ So he agreed to the pact. He conceded that you had something that he didn't, despite how desperately he did want it.
✦ And then you apologised to him. For using dirty tactics to get your way, because you would feel the exact way he did if someone tried to do that with your favourite pieces of media.
✦ …Wait, what???
✦ You actually enjoyed video games and anime too? Just like him??? ...I mean, maybe he could forgive you, but that didn't make you two best friends or anything!!!
✦ Spoiler Alert: It definitely did to him.
✦ He actually got to know you on a deeper level, watching how you'd interact with his brothers, like you were just always meant to fit with them. These… misfit fallen angels that they were.
✦ And the craziest thing of all was that you actually wanted to hang out with him!!! You wanted to share your favourite Human World anime and manga with him, and soon enough (way faster than he was ever willing to admit), he did the same for you with Devildom media.
✦ Which was all fine and dandy, sunshine and rainbows, but why in all of the three realms did his brothers have to be so obnoxious about you? Constantly vying for your attention, while you argued that you'd already scheduled this time for you and him.
✦ And wow, did hearing that pacify his envy quicker than any of the anime merch he's ever bought…
✦ I'd say we're all keenly aware of how annoyed Mammon was at having to babysit the Human Exchange Student. Lucifer is always pushing the menial work off to him, as if he's the only one with more important things to do!
✦ Well, at least you were being compliant and causing little inconvenience to him so far, but really, a whole year of this? Yeah, he was going to drop you as soon as he found the chance to…
✦ …And then you made a pact with him.
✦ Not one of his proudest moments, he will admit, but now he'll have to pay more attention to you, or else he'll just have another person yanking on his chain and telling him what to do! At least, that's what he wants everyone else to believe.
✦ Because admittedly, he was very curious about you. In most social situations you were anxious yet agreeable, but in the moments where you were alone with him, you'd quickly gain the confidence to tease and joke around with him.
✦ And so the first time he sees you genuinely smile and laugh, he already knows that he's a goner. His greed never lies, after all.
✦ And the TSL Showdown sealed the deal for him. He didn't want to see you hurt, because he was the one supposed to protect you, and no one else. You were his problem to take care of, and he was gonna make damn sure that everyone else knew that, including you.
✦ And somehow, despite his foolproof logic, you had seemed so surprised by his confession...
✦ He was willing to accept all the jabs, all the jokes, all the insults if it meant that you would start to rely on him the same way he was starting to rely on you.
✦ He didn't realise it at the time, but he really just needed someone who would accept him for who he was without the constant attacks on his character: A fresh pair of eyes that were able to see him for more than his outward bravado and scummy acts.
✦ You were kind to him, you defended him, and you really seemed to be fond of him.
✦ And his brothers would question why you would defend him so frequently, how you shouldn't feed into his ego when he was so clearly in the wrong, but you would always reason your way out of things. He really started to admire your steadfast and caring nature.
✦ As long as you were there alongside him, he would go just about anywhere and do almost anything that you asked.
✦ The whole Belphie situation left an indelible impact on him. Because first of all, his baby brother had been hidden away without them even knowing (which made him utterly pissed at Lucifer, though he didn't let it completely show.)
✦ And then what Belphie did to you…
✦ Even if you would ultimately end up alive after it all, he doesn't think he'll ever forget the sight of your dying body in his arms, and how it made him feel. He was mourning his human, and he couldn't bring himself to do anything else but sob.
✦ And like everything else in the aftermath of that situation, he just held his feelings back and tried to not let it affect him. Because you were Lilith's descendent, which suddenly made everything better apparently!
✦ …But that did make him wonder; if he felt like this, so distraught and racked with guilt over what happened, then what in all the Three Realms were you feeling?
✦ His brothers mocked him for his stupidity, and while he may get ahead of himself at times, Mammon was arguably the most emotionally mature of them all. It was just as the second eldest, he would hide his true feelings almost as much as Lucifer did.
✦ For the sake of his family, he played the clown. Partially because he was pretty stupid at times, but also because that's just how their family worked. And he was more than fine with that, because as long as his family stayed together, that's all that truly mattered to him.
✦ And guess what? You were part of the family now too: 🎉Congratulations!!! 🎉 So he just wanted to be there for you in whatever way you needed. Just as long as he could be with you, he would be happy.
✦ Just as long as he kept himself in check, and cared for you only as much as you did for him, he could hopefully keep his greed at bay…
✦ At first, Lucifer thought that everything might just go smoothly for once. You seemed generally polite and conscious of your circumstances, not at all like his trouble-making brothers.
✦ But you were only human. And temptations would be around every shadow-y corner of the Devildom... He just didn't expect you to immediately go head-first into the most personally affecting ones for him and his family.
✦ Your spontaneity between acting so innocent and demure to boldly putting yourself in harm's way threw him off in a way he hadn't truly anticipated. Especially with the incident in the Underground Tomb.
✦ You were certainly fascinating, he'd give you that. What was more fascinating and scary however, was the impact you were leaving on his younger brothers.
✦ Mammon almost never left your side, Levi actually made an effort to spend quality time with a non-family member, Beel would now often set aside some of his food for you, Asmo was completely doting on you in a way he never did with anyone else, and Satan had matured in such a short amount of time partly in due to your words of advice and interactions.
✦ He was even finding himself endeared to your earnest endeavour to befriend and understand Demon-kind. For someone who seemed so anxious and doubtful, there never seemed to be a single thought spared to abandoning your own moral code.
✦ And he respected that. He really did, and that was something his pride was slowly coming to terms with. He was starting to personally care about you, not as an Exchange Student, but as the consciously kind and perceptive individual he was now seeing you for.
✦ And yes, this development definitely had a large and potentially lethal wrench thrown into it with the reveal of Belphie's imprisonment in the attic.
✦ He felt ashamed of himself. He had clearly misjudged you all along, and you were just like any other selfish human who was just too curious for their own good. He never used to hate humans, per se, but he wasn't ever particularly fond of them either.
✦ So confirmation bias had hit him hard. Because above all else, he had let this happen. All of it. From the moment he rebelled against their Father, to how he started to soften and genuinely lower his guard around a mere deceitful human, he was the cause of all of these current circumstances.
✦ And Lilith…
✦ He only realized it upon later reflection, but he had always seen a bit of Lilith in you. He couldn't ever pinpoint it, but the moment you hugged him in the Underground Tomb, something just felt right again. After so, so long.
✦ And from that moment on, he ever so slowly started to trust you. You had unintentionally wormed your way into the family, and his brothers were certainly not letting go of you anytime soon. And neither was he.
✦ His respect for you had only grown once he put aside his pride to realise that every single action that you had taken was for the sake of his family. What obligation did you possibly have to do all of this?
✦ Clearly not publicity or fame, otherwise you wouldn't have kept it a secret and downplayed your role whenever you discussed it after the fact.
✦ Of course, an ideal circumstance would have been to gain the favour of his other brothers by saving Belphie, which would easily place himself as the grand villain of the story, and yet you had never used that narrative to your advantage.
✦ When he confronted you about these thoughts, even you seemed a bit uncertain as to why you did it.
✦ Because yes, you may have had your own personal struggles with family and didn't want the worst case scenario that almost happened to you to happen to others, but the complete dedication and tenacity you had for the task surprised even yourself.
✦ And that's when Lucifer knew. Not because of societal status or for any other personal gain: you just wanted to help people. It made you feel happy and fulfilled just to help people and see them be happy.
✦ And how long had it really been since he'd seen such genuine and reckless selflessness right in front of his eyes? The flashes of forbidden Celestial Realm food and a bedridden human in his mind was all the reminder he needed.
✦ So from there on, things were brighter for the both of you. While still reserved, Lucifer was endlessly amused by your interactions and hijinks with his brothers, and would contentedly watch on almost like a proud parent.
✦ Because he was proud to have someone like you as a part of their family...
Quick Note: I wrote this from my own personal experience, so some traits might not fit with your own personal experiences, which is completely Ok! These are all very self-indulgent for me, so I'll be happy if even anyone else out there likes what I've written! - Celeste
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🌟Lucifer🌟
✦ Above all else, Lucifer will listen intently to your personal experiences and directly ask you how you would like your time in the Devildom to be improved
✦ He completely accepts his lack of knowledge in the situation and would consult with both Satan and Solomon about Human mental health and wellbeing
✦ He begins to check in with you on a more consistent basis, making sure you're not overworking yourself and being stressed out by your tasks
✦ He gains even more respect for your persistence and tenacity, and does his best to make his appreciation known with words of affirmation and praise
✦ If he happens to be around when you are in an overwhelming situation, he'll swiftly de-escalate it and, if you would like, hold you close and soothe you with careful repetitive motions
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💳Mammon💳
✦Mammon would initially be confused, but not in the way you might expect, as he had already accepted you for all your quirks and didn't see any issues with your social divergences
✦ He is your biggest hype man, always standing by your side whenever you may need encouragement or comfort
✦ It truly cannot be understated how Mammon will just drop everything in an instant to be there for you when you're feeling anxious, and though he'll never admit it out loud, he's utterly humbled by how quickly you seem to calm down the moment he's in your presence
✦ He has similar issues with focusing and prioritizing work due to distractions (mainly those of the golden variety), so he admires you all the more when you tell him of your silent struggles with your tasks and how you continue to persist in spite of it
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🎮Leviathan🎮
✦ Levi was already aware of your social struggles, as you had both partially bonded over your shared anxiety and awkwardness, but he was honestly quite fascinated about the whole concept of neurodivergency
✦ You would offer him any and all online resources you used to learn about the topic, and you would both end up discussing the finer details of your experiences well into the early morning
✦ He realizes how unintentionally dismissive he's been about your special interests, as he was already wrapped up in his own interests, and resolves himself to always give you a place to gush about your current fixations
✦ (It's with this diversion of his attention that he also realizes that he absolutely adores your excited smiles and giggles, and will never not feel blessed to be part of the reason why you can be so unabashedly happy)
✦ You better believe that when any special occasions roll around, he's pulling out all the stops to get that one piece of obscure merchandise you told him about months ago, because you deserve nothing but his best efforts scouring the internet for Akuzon and D-bay listings
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📚Satan📚
✦ Satan already has some baseline knowledge of the DSM and the different kinds of diagnoses Humans can be assigned, so he's more than willing to get a better understanding of things through a first-hand source
✦ He already had a personal fondness for your physical and vocal stims, and learning the underlying meaning of those actions will end up making him keenly attuned to your comfortability in any social situation
✦ If he notices you wringing your hands or repeatedly shifting your eyes in a tense situation, he's sticking right by your side and giving you gentle and repetitive ministrations to let you know that he's there for you
✦ Conversely, if he sees you kicking your feet with a smile on your face, humming along to one of your favourite songs, it fills him with an intense and almost prideful feeling as he just basks in your presence
✦ He just finds himself feeling soft and fuzzy inside whenever he witnesses your expressive voice and gestures, as he knows it to be very different from how you act publicly, which truly makes him feel special to you.
✦ He's had his own issues with identity and how others perceived him as an extension of Lucifer, so he tries his best to give you validation and reassurance that you are enough; whether you are masking or not
✦ He also completely respects your motivation to push past your anxiety and go outside more often, and will help you in meticulously planning out day trips to both fantastical and peaceful Devildom locales
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🌸Asmodeus🌸
✦ You initially worry that Asmo wouldn't really be able to understand what you're talking about if he hasn't experienced it himself, but his immediate acceptance and willingness to learn more about you puts your anxiety at ease
✦ He knows that he'll never truly understand your experiences in life, and would rather focus on finding out what makes you most happy and comfortable and do all within his power to make it a reality
✦ He always had a way of getting you to confess your innermost issues, no matter how small or insignificant, and allows you a space to vent about the misunderstandings and mistreatment of neurodivergent individuals (and later on with matters of the heart)
✦ He goes on to learn every little detail he can about your fashion sense and what he can do to make you feel pampered and taken care of, so slow-paced shopping sprees and relaxing spa days become a new daily routine for you both
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🍔Beelzebub🍔
✦ Beel is immediately supportive of you and also feels very grateful in knowing how comfortable you are around him and his brothers to be able to tell them something so personal
✦ Early into your tenure in the Devildom, you had already made your highly specific eating habits well known (to your embarrassed dismay at the time), and ever since making the pact, Beel would gently encourage you to try different Devildom foods that he believed would fit with your Human tastes
✦ He understands what it's like to bottle up his emotions to not overwhelm others around him, so he would always be there for you whenever you would shut down and just need a consistent and grounding weight in the form of a warm bear hug
✦ When comforting you, he often asks you about your Human family, and just as much as it's a distraction to help you calm down, it also enlightens Beel to your indomitable loyalty and care for those you deem to be your family (in which he deeply respects your values and feels like a kindred spirit)
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🌌Belphegor🌌
✦ Belphie was always aware of the subtle weariness that permeated your presence despite your bright and happy demeanour, and without even needing to know anything about masking, he would continually invite you to nap with him after dinner (with varying degrees of success initially)
✦ He inherently has a sarcastic streak in him, and while that clashed with your literal interpretation of his words at first, he started to understand your perspective and grew more endeared to your cute pouty reactions whenever he seemed outwardly cold or uncaring
✦ Whenever you were just hanging out with Belphie, you felt comfortable enough to let your mask fall off and relax without worrying about how you appeared to others, with which the youngest brother silently took an immense amount of pride in this exclusivity
✦ He has times where he reflects on how he manipulated you, and how you later confided in him about your fears of being perceived as naïve and idiotic, in which he does all that he can with both his words and actions to show how much he genuinely respects your unwavering kindness and empathy