Why Mui call Giyuu nii-san?

Giyu Tomioka

Strange... they keep following me around...

Giyu Tomioka

(Why do they keep calling me nii-san?)

Kamado Tanjirou

Giyu-niisan! Would you like to join us for lunch?

Kamado Tanjirou

Nezuko made special onigiri!

Kamado Nezuko

Mmm! Mmm! (Giyu-niisan, please eat with us!)

Giyu Tomioka

I... don't understand. I'm not actually your...

Muichiro Tokito

Oh? Are we calling Tomioka 'nii-san' now?

Muichiro Tokito

(Looks fun...)

Giyu Tomioka

Tokito, don't you dare...

Muichiro Tokito

Giyu-niisan, wait for me too~

Giyu Tomioka

...I give up. Do what you want.

Giyu Tomioka

(Why did I become everyone's big brother suddenly?)