Responses
https://www.mangago.me/read-manga/dark_heaven/
both in a band- one plays the guitar and one sings
https://www.mangago.me/read-manga/there_s_something_wrong_with_my_popularity/ this story’s side couple’s seme is in a band but they’re introduced in the latter half
bl manhwa [not manga] with one of them being in a band, or plays guitar