Hori Erio manga
Yui has a small body but has always wanted to have a big, muscular body. He enrolls in a gym with his idol as his instructor, Tachibana. Also contains another oneshot called Taberarechau!: Yuu moved in with his relatives because his parents moved south for their jobs. A friend warned him about his cousin Hiromi, who seems to be going out with a guy.
From Midnight Scans: A quiet girl falls in love with a fourth year ikagu club member, Koushirou-san, who is a kind, serious, and charming person... But then... why would he...!?