Houkago, Boku wa Kimi ni Naru

Akiba, a high school boy who has become addicted to cross-dressing cosplay, devotes himself to emulating his "oshi." Then one day, while he was dressed up as his favorite character, all alone in the club room, he is found out by Shibuya, a gorgeous gal that he has a crush on...? This is the start of a secret relationship between these two polar opposites! They will apply their youthful enthusiasm to a life of "oshi promotion"!

https://www.cmoa.jp/title/301113/