Aisareru Karada

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.