Idea dump

Upper Moon zero

This is a demon slayer idea I've had for a while. I thought of the idea because of how in some shows like Bleach and One piece there are these numbered teams (Cipher pol and the Gotei 13) and then it's revealed there's a secret team that's numbered zero (Zero squad and Cp-0) so I decided to make my own.
The book will be spilt between Tanjiro's and Upper moon zero's point of view. I'll try to give some information with giving too much of the plot away also I don't have a name for him yet so he'll be called Rei (a way in Japanese to say Zero) for ease, and warning I will try my best not to but there may be some spoilers for the manga. Rei is obviously more powerful than the Upper moon 1, however he's so much stronger that like Muzan his blood will make a demon stronger it's also said that like Rui Muzan has given Rei permission to give his to demons and a lot of demons seek to get both Muzan and Rei's blood. Rei has spots in Japan that are his territory and all other demon even the Upper moons are forbidden to hunt humans in his territory. He's like Akaza as both have a rule on eating humans i.e Akaza doesn't eat women and Rei will only eat Demon Slayers. According to Rei the rank determines how filling they are, a simple explanation is Mizunoto (the lowest demon slayer rank) are like a light snack to him, Kinoe (the kind-of Highest rank) are like a nine course meal to him, and Hashira are like eating an entire banquet by himself. This has a both good and bad result as Rei will keep high rank Demon slayers alive and feed on them later; this is bad because well the slayer is slowly being eating but good because if fellow demon slayers find the captured slayer they can be set free and Rei has been know to accidentally reveal information about his fellow Twelve Kizuki to a captured slayer. His rule to only eat demon slayers means he eats active demons slayers which means he won't eat people like Aoi as though she technically is a Mizunoto ranked demon slayer due to passing Final selection she does not fight demons, Urokodaki, as although he was a Hashira he is retired and while he most likely can, he doesn't hunt demons, and the Ubuyashiki family as even though they lead the Demon slayer corp for the reason stated before.

Ok, here a few big one's, Rei has a Nichirin sword and can use almost every breath style and techniques (before anyone asks yes he can use Sun breathing). The only ones he can't use are new created breathing style and/or techniques like Beast breathing, because of this he is obsessed with finding new ones so much so he will actually let Demon slayers go if they created/have a new breathing styles. He also brakes their weapons to acquire their breathing style. He is unkillable as he was one of the first people if not the first person Muzan turned into the a demon, as such he has built up a resistances to Sunlight, Wisteria poison and Decapitation. I only made the Wisteria thing up as in canon at least two demons have become immune to sunlight, and at least four possibly five demons have regrown their heads after decapitation (Rui, the Upper moon six demons aren't count among these demons as Rui survived decapitation via a plot hole, and Upper six will die if both are decapitated, while these demons had thier heads cut off and regrow them so they only die from wisteria poison or sunlight). The demons slayer corp fears him so much that in the past 5 Tsuchinoto (the fifth rank) demon slayers each have a heightened form of one of the five senses ( i.e. heightened smell, hearing, touch, sight, and taste) volunteered to go on a suicide mission to be able to tell when he's near via his scent, the sound he makes when he moves/his voice, the feeling, and taste of the air when he is near, and the most risky of all getting a look at his face as Rei can disguise himself but certain facial features and his movements do not change. They succeed in their mission and what they described about him was give to all current members and will told to any future members. This information told to members so if they can avoid him. Also I'm thinking of giving him Japanese funeral music as a theme because 95% of the time he shows up most of the people if not everyone he sees is going to die