Seraph of the End x Demon Slayer OC's

An unknown virus has spread. Killing everyone over the age of 13.
((In the city))
[Almost everything is canon] Kids tried to hide from the vampires with no luck. Mikaela turned into a vampire later on while Yuichiro joined the Moon Demon Company. Then a war between vampires and humans have started... again. The humans retreated due to lack of comrades. Until unknown people more like teenagers had wiped out more than half of the vampires fighting at the moment.

(All the demons died because of the virus since the demons are more sensitive to the virus even if the virus was about 5km away from them. Nezuko died too while she was in the middle of transforming back into human. The humans from that range didn't die though)

((In the mountains))
The crows have reported that people are dying, specifically over the age of 13 due to the unknown virus. Though it didn't effect anyone who lived in the mountains, specifically the one called THE MOUNTAIN VILLAGE. Teens, adults even elderly are still alive in that village. It was said that the virus killed only the ones near the entrance of the mountain. What surprised them is that demons, uppermoons and even the man himself, Muzan, died during the battle and it was still night. Though the fight was 1 month ago (The fight was at the mountain as well but far away from the civilization). None of the Demon Slayers were hurt during the fight and Master Ubuyashiki's sickness was healed because of the virus which was weird. What hurt the most for the 3 kids is that their parents, who were forever best friends, were in the city that night, meaning they had also died. After a few more depressing days, the three children have decided to part of the corps even if there are no more demons they are still to fight the vampires that they later discovered.

Yeah, I don't own anything except the oc's, the plot and other things that may be added later on are mine.