5(Demon Slayer)

An AU where Tsukato survives as a demon slayer, maybe Urokodaki, arrives in time to kill the demon before she is killed so Tomioka still has his sister and brother-in-law(whose name and appearance are up to the writer since I don't think it was mentioned in canon).

Of course that the attack of the demon brought some trauma(and damage...maybe Tsukato got a scar or something) which Urodaki tried to help them but at least informing them that demons can't deal with wisteria but when Tomioka was a few years older, he requested to be trained to become a demon slayer so he could protect his family especially his future nephews and nieces.

Tsukato and her husband feared what the life of a demon slayer might bring to Tomioka but knew that he was stubborn so they gave him their support and visited him often while he was training under Urodaki(it follows canon in Giyuu and Sabito becoming best friends but if Makomo survived and visited her master and met them is up to the writer).

How the final selection would go is mostly up to the writer but even if Sabito died, Tomioka would have Tsukato and her husband there for him so he could still become a bit closed due to trauma but not as much in canon.

Anyways, Tomioka became a pillar and while not super social, he still talked with the other pillars who mostly assumed he was more of a loner and didn't want anyone around him.

So imagine their surprise(if this is before Kanae died, or if she died, or if after Tanjiro's trial is up to the writer) when one day after the end of a reunion as they were leaving as a group, two kids run to Tomioka calling him 'Uncle Giyuu' while being followed by a older female version of Giyuu(but without the spiky hair) and a man with adding that Giyuu smiled at them(not a small one, a big happy one).

Basically, I want Giyuu to have his sister still there for him and watch the pillars reaction to their 'emotionless' water pillar being a softie for his family.