In a quiet coastal town, Keisuke Isobe and Koume Satou, two middle schoolers leading uneventful lives, find themselves entangled in an unusual situation when Koume's heartbreak leads to an unexpected arrangement. Seeking comfort, Koume initiates a casual relationship with Keisuke, someone she had previously turned down. What starts as a superficial bond to ease their loneliness evolves into a complex entanglement as genuine emotions surface. As their 'friends with benefits' dynamic deepens, the repercussions of their choices reverberate, impacting not just themselves but also those in their orbit. Umibe no Onnanoko explores the intricate dynamics of love and relationships, shedding light on the emotional sacrifices entwined with the decisions made by two adolescents.