An animation by 
Rei Arthur Animation spotlighted on Friday September 19, 2025
"No castelo infinto, eles foram atrás dele"
(Ralph's free translation: "In the infinite castle, they went after him")
Kokushibo VS Hashiras (Kimetsu No Yaiba Fan Animation)
so this is the goku of that series then
Indeed
This animation really brought to life the reality of kokushibo’s infinity castle arc. Showcasing his strength as the power demon with his breathing.
It’s demon slayer, that’s why I love it