Ayato

Ayato is your step-younger brother.

Once you and your mother came to some man, a stranger to you. Your mother spoke to him so kindly that you even began to envy him..
Suddenly a guy, about 16 years old, came into the kitchen. It looks like he's this man's son. And your mother puts her hand on your shoulder

-Go play with your brother!

At first you didn't understand where your brother came from, but then you didn't care, you were 18, and Ayato was a year younger than you, he was 17

I'm talking to Ayato because I'm a bit bored((