A Girl on the Shore (2016) GN

Koume Sato and Kosuke Isobe are two teenagers living in a sleepy Japanese seaside town. After getting used and dumped by her crush, the emotionally damaged Koume decides to start a relationship with Kosuke, without any emotions involved. However, they both soon discover that sex with no strings attached often leads to unexpected complications, not just for themselves but also the people around them. Rated for ages 18+.