From MangaHelpers:

Hayase Hitomi is a high school girl who has been in love with her older brother, Hijiri, since they were children. Hijiri is currently in college, studying to be a teacher. In an attempt to get over her brother, Hitomi ends up dating Kazuki, an older boy she meets in a karaoke group outing. Kazuki is very physically pushy, but Hitomi assumes this is normal when people date.

However, their short relationship ends with an unmistakably criminal violation of Hitomi. Now, she keeps the reason for her pain secret from the people who care about her. Things only get more confusing when her brother and his classmates from college arrive to student-teach at her school. The student teacher in Hitomi's classroom is Ayane, a pretty young woman who clearly likes Hijiri. Will Hitomi be able to sort out her feelings for her brother and overcome the trauma of what was done to her? [tethysdust]