So because the original version of this post was acting up and not functioning with editing; Spider Mod's notes had to be remade. Like with the original this will more than likely be added onto as time goes on.
Spider Mod Notes Remake:
Rui bites when he feels threatened and/or if he feels it is necessary, Evidently his bites are venomous depending on how threatened he feels
He is very ticklish on his facial-markings, hands, feet, sides and tummy. His laugh is very squeaky when he is being tickled. And he does like being tickled but only by certain people, anyone else usually gets either scratched or bit. Booping him on the nose will also get him to laugh but follows the same rules as his ticklish spots but a bit looser.
Thanks to certain older members of the Kizuki lacking a verbal filter, he knows swearwords and will use them as and when he sees fit. Despite this he does not understand adult jokes or concepts and may ask older moons what they mean.
Due to his poor vision and what remains of his breathing problem from when he was human; he trips and falls a lot, and when he does he tends to lay there for a minute or so stunned and trying to get air back into his lungs before trying to get back up.
He loves attention and tends to be a bit of an attention hog when it comes to people he cares about. He loves being held and getting as many hugs, head-pats and face-squishes as he can get from those he cares about. However if someone he doesn't like does any of these he will more than likely bite them.
While he has been doing his best to improve and be better behaved, he still feels very guilty and embarrassed about how he treated his adoptive family. He is now very protective of his adopted family and his friends
Due to how he was "raised" by Muzan and the older moon's he is very awkward with apologies and he will either over apologize or be barely able to get it out with no inbetween but he is trying.
Even before trying to turn over a new leaf, He was considered one of the least hostile moons as whenever someone entered his forest he would not attack someone unless they were purposefully causing a ruckus or he got hungry. Otherwise he would tell any visitors to leave, have the spiders chase them out or let them stick around and have a chat.
That said, while he is among the least hostile moons; he still can and will be very cruel and ruthless with anyone who deserves it and even more so if they give him a reason to be mad.
Due to him starting to help out the towns at the base of his mountain with their respective bandit problems; he and his family are eating well and willing to share with demons in need of a meal.
Over the years he has developed several spider like traits, including but not limited to; being fond of shiny things and using them to attract his prey, being able to breath underwater for half an hour, hating sudden loud noises, ect.
Aside from spiders his favorite animals are rabbits, cats, mice, crows and raccoons. He loves all animals and treats them all kindly but he is terrified of snakes, largely because his poor vision makes it difficult to differentiate between a snake on the ground and roots or weirdly shaped branches and will react to snakes by getting himself as far away from them as quickly as possible.
When he was human his favorite foods were chocolate, strawberries and pork-buns. Because of this he occasionally gets into his older sister's cocoons as they are similar, however he is trying to find an alternative because webbing is decidedly inedible and hard to get out of one's fangs. On the other hand he could not stand watermelon or anything with either very little flavor or a very bitter flavor.
Over the years he has picked up a lot of hobbies, most of them are in the same vein; weaving, beading, knitting, crochet, sewing, ect. But he is also an avid reader (always has been) and has developed a fondness for pranks due to being surprisingly mischievous. He has also developed an interest in human-watching through the eyes of his spiders, finding them interesting and often quite funny.
As he was turned as a child, he is still very childish. He loves playing with and receiving toys (even if he tends to accidentally break them), he collects plushies like a dragon, he swings his legs when he's sitting in a high place, he mis-spells and mispronounces new words before inevitably trying to sound them out, still believes in classic holiday icons and he plays pretend when he thinks nobody important is looking.
He has an interesting rivalry with Upper Five (Gyokko). To put it simply they hate each-other and have since Rui first became a moon. Because Gyokko tries to cause him harm or get him into trouble with Muzan and Rui responds with pranks that usually involve messing with his artwork or messing with his mind.
Because he is one of Muzan's favorite moons, he is not above being a tattletale or otherwise using his favoritism status to his advantage especially if he knows he can get something good out of it. However he does also weasel his way into getting the other moons to owe him favors incase the favoritism status does not work.
There is one surefire way to get him to calm down and even get him to fall asleep when he is anxious or generally upset about something: Holding him close enough to hear one's heartbeat, tracing his facial-marks, and humming a lullaby.
You can always tell when he is frightened because his hair will poof up either slowly or quickly depending on how quickly he gets to the point of bolting and he will squeak when he gets startled.
He does not trust adults (for good reason) and when interacting with adults they have either pose very little threat to him or make a good first impression on him to gain his trust, and if they lose his trust for any reason or give him a reason to not trust them in the first place; he will never trust them. But more than other adults he does not trust doctors (not in the sense that he does not trust medical science, he actually finds medical science itself rather interesting, it is the people themselves he does not trust) due to trauma involving an abusive doctor when he was human.
He likes the neighbors he does have (Douma, Enmu and Akaza) well enough but he does wish that some of them would not get so reckless and rowdy with their fighting that they destroy parts of the forest.
He will actively try to be intimidating but he tends to forget that he is 4'5 and as intimidating as a kitten. His intimidation tactics only work on lower ranked slayer and easily intimidated demons.
He has dug tunnels that go for miles across japan that he takes when he needs to travel during the day or if he needs to get somewhere quicker than usual. If he needs to get somewhere that is above ground quickly then he will Kite/Balloon there with his webs.
He keeps a journal in which he writes anything and everything that comes to mind that seems like it could/would be important. He always has it either on his person or close by and if someone who does not have his permission touches it, it gets shredded to pieces by the spell he placed on it by taking a page out of enmu's book and infusing a few drops of his blood with the glue holding it together.
He has unlocked his "Final Form" and similarly to his normal demon art's uses it however and whenever he pleases.
(Due to a theory about how BDA's work that i use frequently on this blog I'm adding this here) Due to how blood works and how blood demon arts work; Whenever Rui gains a new family member and shares one of his demon arts with them he loses it temporarily but he gets it back after about a month. Though there are a fair few he tends to dislike using
When he gets nervous he bites his nails/claws. But he is unashamed to admit that he paints his nails/claws teal to try to stop himself (it hasn't worked yet) and to make it easier to see the starts of his threads.
As long as it does not poison him or make him ill, he can and will eat anything he can get his fangs on if he is hungry enough.
He is an adorable little menace upon society and he knows it. As such he acts accordingly.
So this one is a little awkward, as before I incorrectly referred to this as a ship or as Rui having a, secret but completely innocent crush on Daki because the demon slayer fandom doesn't have a term similar to "moirail" like one of my previous fandoms homestuck does, and it taking place in the taisho era made it feel off to use the term "moirail". But I have since decided to say screw it and use the term anyway. I feel like Daki and Rui would have a Moirail-like relationship or a Moirailegence (moirail definition: your soul-mate in the non-romantic/platonic sense. The person who balances you out personality wise and makes you feel complete. But way closer than just best friends. The ultimate friendship bond.) so that is what they have on here.
He shows people he cares about them by making or getting them things for any reason he can come up with and often no reason at all. He also likes giving nicknames as a way of showing that he cares but coming up with them takes a while and usually happens at random.
He is very fond of butterflies and forget-me-not flowers because they remind him of his parents. His father loved forget-me-nots and his mother loved butterflies because they reminded them of him.
He has a separate notebook he allows the new demons he takes in to read that functions as a guide to living as a demon. Linked here
There is a reason why I compare him to a cat/kitten, because spiders are essentially the cats of the insect world; they share many traits and as such our dear little spider demon also has some more cat-like traits.
While he can shrink himself down to be smaller or look younger, due to the fact that he was turned at the start of puberty which he likely would not have survived due to the strain it would have put on his already frail body he cannot make himself bigger or look older despite getting hungry easier and needing to eat more than he did before he was turned; because his body has no idea what it is supposed to be doing since it can no longer age as it is supposed to especially at his age. This is also probably why his emotions are a bit more explosively all over the place than most others. Basically he is in a constant state of being a "growing boy" without actually growing.
Because he can only remember some parts of his past, he remembers that his human parents are dead and that Muzan was there when they died. He does not remember that he is the one who actually killed them in an act of self defense that accidentally went too far due to an inability to control his new-found strength and instead thinks it was Muzan who killed his parents.
He has given his cats, mouse and frog vitamins and vitamin heavy foods to increase their intelligence which works fairly well since they are demon animals.