The Child of Darkness (Demon Slayer Role-Swap AU x OC)

What if the Kamado Family adopted a child the same age as Tanjiro and Nezuko, the twin eldest siblings of the house?
What if Tanjiro returned home earlier instead of staying at Saburo-san's?
What if Nezuko left the household to deliver some kimonos and stayed at Saburo-san's?
What if Tanjiro's new adopted brother became a demon trying to protect his new family from Muzan Kibutsuji?
Everyone is dead.
Except for Nezuko.
Except for Tanjiro.
Except for Tocho.
The triplets must survive together, using their combined heightened senses to survive in this cruel, cruel world.
At least, that's what they thought.
Until Tanjiro turned into a demon and lost his wits.
What will they do when Giyu Tomioka arrives, threatening to kill not only Tanjiro, but Tocho as well?
How does Tocho keep his wits but Tanjiro doesn't?
Only the Author knows the answer to these questions.
Click on the 'Read' button to find out more.

Disclaimer: I am not Koyoharu Gotouge, I do not own Demon Slayer, I only own Tocho, and the altered versions of the original plot, not even the concept of Nezuko's heightened sense or Tanjiro's demon nature is mine, I first got the ideas from Novirp13 on Fanfiction.net, so you can check out their story too. All images belong to their respective creators, since I can't draw to save my life, the only thing I'm good at is making collages.

Note: I'm following on from the Anime. Not the Manga. The Anime. Keep that in mind as you read. Because honestly, I can't be bothered correcting people when they tell me something's wrong. It's a fanfiction, for god's sake! Stuff gets changed anyways, so why care? Also, I'm toying around with the ages a bit and altering Nezuko's appearance. Nezuko and Tanjiro will be the same age, but Nezuko being born a few minutes later than Tanjiro, Nezuko will also have red eyes and red hair. Tocho has the same birthday as them, too, so they can really be called triplets.