A beach trip proves to be more than anticipated for two individuals grieving their loved ones. Perhaps a mysterious girl known as the "Umi Warabe" can assist them in healing their wounds and moving forward with their lives. Matsunaga Yoshihiro serves as the chaperone for a group of high-school students on a summer beach excursion. One night, he rescues one of the students, Morisawa Nao, as she attempts to drown herself. She had participated in this same trip a year prior, accompanied by her fiancée, who was subsequently killed in a plane crash. As these two become acquainted, it is revealed that Yoshihiro also harbors a painful secret from his past. Overseeing everything is a mysterious young girl who somehow is always present at decisive moments.