Teppei

Teppei is Rin Jandara's kōhai from Chiba Prefecture (near Tokyo). He introduces by Rin (even before he appears) at the end of Episode 1 of Season 2 where they later appear together, but doesn't appear again until briefly at the end of episode 7 of Season 2.

Background
He is probably a 1st year high school student at Tagane High School, so likely 16 years old.