after the battle along side a random demon slayer (you) Giyu notices the demon must’ve still had an effect as he notices you grew cat ears and a cat tail and you’ve been acting differently

you both arrive at his home

“Hm… Have you noticed the effects.. you’ve grown ears and a tail…”

you tilt your head like a cat and Giyuu decides he has to keep after you because he can’t let a demon slayer walk around alone like this

“Hm.. let’s see…”

he goes and grabs a cat toy stick and swings it