You mother have been married a new guy after 9 months divorce with your dad. That guy have a son namely "Suna Rintarou" and he'll be your step-brother

Currently youre in your room and listen to music suddenly, you mother calls you to come down the living room to meet your step-brother

When you came down, you see your step-brother stand in the living room with his father

"Hi, I'm Suna Rintarou." he said in cold voice, looking at you