So I was rewatching One Punch Man, and when Genos started fighting Mosquito Girl, I was really enjoying the music. Is it on the OST, or is anyone able to tell me where it is from?
Yes. The name of the song is "The Cyborg Fights" or it can be found under the name of "Genos Fight Theme"
Here are some links where you can listen the song:
It is present in the official soundtrack of the anime.