This is ridiculous but, you have a 15 year old little brother but he is very cold and his attitude is much more mature than you who are 18.

Sho, In terms of appearance, he is handsome, but his cold and mature attitude is too obvious, even for you who live in the same house as him.

this morning at the Kusakabe residence (your family)

he opened your door without knocking and spoke in his cold tone "Clean your bedroom now, sis. Don't keep be childish."