the true demon king Tanjuro/upper moon 1

Tanjiro turns nezuko into demons/nezuko turn zenitsu into a demon

Tanjiro was born with four demon slayer mark on his forehead and Tanjiro has demon king eyes and demon fangs and kie said I will not raise him at all and Tanjuro said I will also now raise him either and so they both decided to raise Tanjiro until he can walk and talk on his own then they will start abused him and over time nezuko,hanako,rokuta, Shigeru, takeo were born and kie and Tanjuro treated them with love and happiness but not with Tanjiro and they would even put Tanjiro in a room away from his siblings and some times Tanjiro would go out and kill humans to eat because his parents don't feed him at all. Nezuko would sometimes wonder who is in the room which they are not allowed in or near so one night nezuko woke up and sneak away to the room and when nezuko try to open it it was locked so she had to go back to where her parents were to get the keys and when she unlocked the door and opened it to find Tanjiro sitting there and nezuko said um hello and Tanjiro turns around and sow nezuko and said why are you here nezuko you should be asleep with the rest of the family and nezuko said but you are part of our Family and Tanjiro got up and said I am part of the family but I am a demon king so I am not human and I eat humans to stay alive so you should leave now and nezuko was shocked and left the room and went to bed and in the next morning kie goes to Tanjiro room and abused him until it is evening and same with Tanjuro and nezuko visits Tanjiro at night with Hanako and Rokuta and over years the visits from nezuko, hanako, rokuta and abused from his parents became daily and Tanjiro became immune to the Sun and Tanjiro had enough of the abused so Tanjiro decided to leave with nezuko and hanako, rokuta and that night when they came Tanjiro told them and they were happy so they left and started packing and after about 9 minutes nezuko and hanako were ready and Tanjiro said fellow me and they did and they went to the entertainment district and Tanjiro creates a hole and told them to get in and fellow me and they did and walk for 99 hours until Tanjiro jumps down and then creates the Infinity Fortress

And Tanjiro said this is our new home and nezuko said can you turn humans into demons and Tanjiro said yes I can so nezuko do you want to become a demon and nezuko said yes and Tanjiro gives nezuko his blood and nezuko started aging and had fom in her mouth and she passed out and after about 100 hours nezuko woke up and was a demon and Tanjiro said nezuko you are upper night 4 and I will train you how to use your blood demon art and Tanjiro walk into a room and nezuko fellow and over years nezuko now know how to use her blood demon arts and went out and started killing humans and eating them and Tanjiro went out and started killing humans for years and years

Minwhille with nezuko
Nezuko went to mount natagumo and was walking around until she found 100,00 demon slayers and nezuko killed all of them and then started eating them all and then heard a scream and nezuko went to the noise and hid behind a tree to see a boy with yellow hair screaming and complaining about something and nezuko found this cute and annoying at the same time and nezuko came out of hiding and went up to the boy and said hello my name is nezuko Kamado upper night 4 what is your name and the boy said oh my name is zenitsu Agatsuma and they started talking for hours and then nezuko said why don't you become a demon then we can spend more time and zenitsu said yes and nezuko gives him her blood and zenitsu started turning into a demon and then 23 demon slayers came and nezuko said zenitsu try to use your blood demon art and zenitsu did and killed them and nezuko ate the rest of the demon slayers that she already killed and finish and so did zenitsu and they came back to the Infinity fortess to see Tanjiro and Tanjiro said zenitsu you will be upper night 5 and will be conceted to nezuko and they both bow down to Tanjiro and they spend more time together and over years they fell in love with each other even more

Back in the present
Tanjiro now have more upper nights and lower nights and everyone lived in their place that Tanjiro has assigned them and has killed hundreds thousands of humans and demon slayers and the leaders of the demon slayer only know about muzan being the demon king and knows nothing about Tanjiro being the ture demon king and over years Tanjiro has watch muzan make some people into the upper moons so Tanjiro decided to join muzan but Tanjiro has summon all the upper nights and lower nights in the Infinity Fortress and  Tanjiro told them that they will stay in the Infinity Fortress while he stays with muzan so that muzan or the upper moons find out about him being king then there will be a war between muzan and Tanjiro and everyone agrees to stay in the Infinity Fortress and still kill humans at that and when Tanjiro went on a walk in a town and fight some humans and killed them and that got muzan interested so he came to the town and found Tanjiro and gives Tanjiro his blood and muzan said Tanjiro kamado you are upper moon 1 with Kokushibo and Tanjiro just smark and said let's do this and they went to the Infinity fortess with muzan and these backstory of every upper night and lower nights and how they met Tanjiro