Umanbo!

Ushida Mansaku, following his family tradition, became a boxer, but his career is a succession of defeats. After one last loss, he decides to run away and starts a new life living as a woman. Eventually, he became an office lady in a big company, under the name of Ushida Manko (Myriam), where everybody sees him as a beautiful, warm, and gentle OL.

Note: Release dates are based on the tankoubon volumes.