A guitar riff playing in episode 80 and 85 of My Hero Academia season 4 In My Hero Academia season 4 episode 80 at around 3:05, there's a guitar riff playing. The same riff is also playing in episode 85.

What is this OST?
Maybe this is Sorezore no Mokuhyou (Spotify link)  by Yuki Hayashi, the 5th track in Boku no Hero Academia Season 2 OST album.