Mitsuka Yoshimine is a teacher at Koharu High School, where she instructs English. She is an attractive woman with long black hair and brown eyes, often seen wearing a suit and pumps. She is both intelligent and resourceful, but her most defining trait is her shameless exhibitionism. She spends far more energy devising ways to show off or provoke her students than she does actually teaching. Her flirtatious and provocative behavior frequently creates awkward or embarrassing situations, especially for the main character Takeya Ikuhara and those around him. She has a habit of misinterpreting ordinary conversations and events as sexual in nature, which often unsettles others.

Despite her outwardly unserious demeanor, Mitsuka occasionally displays surprising insight into interpersonal relationships, particularly regarding the bond between Takeya and the DearS girl Ren. In these moments, she offers observations that reveal a deeper understanding than her antics might suggest. She also works as a porn actress, and a substantial section of the local video rental store is dedicated to films featuring her.

Mitsuka is a supporting character whose presence provides comic relief through her over-the-top flirtatiousness and tendency to catch the main cast in mortifying situations. She does not undergo significant character development over the course of the story, remaining consistently provocative and resourceful. Her notable abilities lie in her quick wit, her talent for manipulation, and her knack for appearing at the most inconvenient times.