Ok so decided I'm going to post my half-demon headcanons 💃💃💃
KNY Half-Demon Headcanons
• Slower aging. Can still die from old age eventually, but it will take a very, very, very long time till that happens. Idk current idea is that they age normally until around puberty their aging starts to slow more and more until into adulthood where it would roughly take 10-15 years to age 1 year physically. Subject to change because I'm awful at math.
• Can tolerate being under direct sunlight for a certain amount of time (current idea is roughly around 20 minutes or so give or take) before becoming incredibly weak and lethargic, then the skin starts to blister and boil, and finally the body starts to disintegrate and burn away. They don't instantly burn away into ash like demons, instead it's a slower process and could possibly be stopped if taken under shade in time. Regeneration/recovery from such an ordeal is a whole can of worms entirely depending on how burned and disintegrated the half-demon is. Any Blood Demon Art used under the sunlight will also be weakened (varies in how weakened it is by the amount of sunlight and the strength of the user). So they can technically be out and about during the day, just as long as they can frequently get breaks away from the sun. Had an idea that the sunlight tolerance can be extended if exposed to it enough though it will not only take a very long time for there to be any significant change, but needs a whole lot of consistency too. Kind of like building up an immunity to something or like exposure therapy.
• Don’t need to consume human flesh and blood to survive as they can eat and gain nutrients from human food, but tend to be more carnivorous and prefer raw meat (and probably need to consume more meat than humans anyway). The more fresh the better. Are still able to survive off of human flesh and blood if they really choose to do so.
• Do need to sleep, but only about once or twice a week. Can suffer from sleep deprivation, but it will take far longer for any symptoms to occur than in humans.
• Tend to have some demonic instincts such as the urge to hunt and kill. Can get stressed and antsy if unable to for a long period of time. Also naturally have some instinctive combat skills (Nezuko seemed to instinctively know how to defend herself and others after just turning e.g. her first encounter with Giyu and the Temple Demon. Or at least tried to). A newly turned full demon would still be a bit more proficient at fighting than a young and/or inexperienced and untrained half-demon.
• While they may be Half-demon, they are also Half-human. Make of that what you will. Generally speaking though, I think most half-demons would lean more towards a human morality and mentality. Of course humans are complex and there is the good, the bad, and everything in-between to consider. And the environment that they're raised in will affect them too. There can easily be a half-demon who has no qualms over hurting and killing humans for food, fun, or simply because they can just as there can easily be a half-demon who will do everything they can to protect humans or a half-demon who doesn't care about the affairs of both humans and demons.
• Faster healing than humans, but not to the extent of demons (could possibly take days to regenerate a lost limb, though it can vary from individual to individual and if there's medical aid involved). Any extreme injuries or mutilation can result in death like being bisected in half or something to that extent.
• Stronger, faster, and more heightened senses naturally than the average human (not as strong as a demon's by default). With training and practice these traits can improve. I dare say they could have the potential to be on par with some of the Kizuki! We've seen in canon the Hashira/the Kamaboko Squad being able to keep up with Upper Moons even for just a while. And they're just humans by the end of the day. So I don't think it would be out of the question if a half-demon were to train extensively in a similar vein for them to be as powerful, if not more so due to their demonic traits.
• Potentially can have Blood Demon Arts, though only half-demons sired from a Kizuki or exclusively the Upper Moons are able to get them (leaning towards only the Upper Moons). Depending on how exactly BDAs work, said half-demons could have similar or related BDAs to their demon parent with exceptions. (I tried making both Aina’s and Sayaka’s BDAs somewhat related to Hantengu's albeit through elements since he/the clones wield some (lightning, wind, sound, wood/flora))
• Speaking of, half-demons sired from the Kizuki are more likely to be stronger than those sired from regular demons. Makes sense ¯\_(ツ)_/¯
• Half-demons can exhibit some of the physical traits that their demon parent has, but toned down a bit. Most, if not all, half-demons only have 1 set of fangs (unless said demon parent has different kind of teeth like Gyutaro and his mouth full of sharp toothies)
• Can vary from individual to individual, but generally half-demons struggle with flesh manipulation. Takes a lot of energy, time, and effort to be able to do anything substantial beyond masking demonic traits and maybe some blood manipulation.
• Wisteria isn't exactly super toxic/poisonous to them when injected or ingested, but it can still have an effect on them. Though more like in the way alcohol and drugs affect humans. So yeah half-demons can get high or drunk from wisteria depending on how it's consumed/prepared. Obviously in large quantities it will impact them more negatively similar to humans. May be susceptible to addiction. Touching wisteria for a certain amount of time can lead to rashes developing as well.
• Half-demons are usually sired by a demon father and a human mother and rarely at that. Extremely rare for a female demon to fall pregnant. Even more rare that the pregnancy goes full term due to the body naturally absorbing the fetus once it starts developing. So yeah practically impossible for a female demon to get pregnant.
• Half-demons can breed with humans and demons. Easier with humans than demons, but not guaranteed since half-demons have a far lower fertility than humans (obviously not counting humans who do have fertility issues and such). They may even have a lower fertility than full demons since they're hybrids (maybe idk not too sure on this yet).
(I've had thoughts that they are straight up infertile or sterile (don't know which term is more accurate), but my self-indulgent brain drabble of Aina being a mom stopped that lmao.)
• I kind of forgot that demons could do this (or rather other demons besides Muzan), but the psychic information sharing thing! Yeah unfortunately don't think half-demons would be able to do that. Both receive or send their thoughts. Maybe at most be able to kind of project their emotional state?? Idk
• Pretty sure I got this idea from someone else's half-demon headcanons (specifically for their OC, but I don't remember who right now), and I'm not 100% sure about it for my own version of half-demons, but the possibility of them being able to go in a berserk mode/have an advanced form. Similar to what Nezuko has (and other examples I'm currently not thinking of or can't say for spoilers). It wouldn't be as drastic of course, but they would end up with more demonic features (said features from their demon parent) and better…well everything. Strength, healing, reflexes, etc. Again not too sure on this yet, so take this point with a grain of salt.
And that's it for now! No doubt there will be updates if I do get more ideas or want to make changes.
