The hashiras are not dead but Tanjiro has become the demon king and now they have to fight him or be turned into demons and rengoku isn’t dead and tengen hasn’t retired

Shinobu was making a poison but you walked in and coincidently she knocks over a potion that makes her a toddler and y/n a baby

You got brainwashed by a demon

Giyu is eating ramen with tanjiro after the final battle y/n was his best friend but she died with shinobu against douma

Basically you and shinobu were besties and you became a demon and she was there but you ran away and now your upper moon 5 and you two meet again

He wants all of you to say all hail diddy

Shinobu y/n (you) tanjiro nezuko zenitsu Sanemi and muichiro are not infected the infected are genya inosuke kanao Giyu and Obanai Mitsuri is showing symptoms