My Coworker Has a Secret! manga volume 1 features story and art by Mushiro.

Akari is an average 25-year-old office worker who harbors a secret she hides from her colleagues: she's so obsessed with the pretty-boy idol Ren-Ren that it's ruining her financially!

When her lunch is stolen by a pigeon, a kind stranger offers his homemade bento in its place, and after graciously accepting, Akari tells him the reason she's so destitute. It's the first time she's revealed her secret otaku lifestyle to anyone. Of course, she assumes she'll never see this stranger again... until he shows up as the newest employee at her office! Can Akari trust him to keep her tragic and embarrassing secret from their coworkers?