On that day, I did hear it. The tidal wave that changed my destiny.

Tamao Kashiwagi is a twenty-seven-year-old woman who has withdrawn from social life, a so-called mourning woman. Having lost her parents as a child and subsequently endured unkind words from relatives, she developed a deep difficulty in speaking to others. One day, she encounters a young boy named Umi who is living through a similar circumstance of loneliness and familial absence. Seeing her own painful past reflected in Umi, Tamao makes the life-altering decision to take him into her home and become his caretaker.

The story follows the delicate and challenging cohabitation of a mourning woman and a gloomy young boy. Their daily life together is fraught with difficulties, as both struggle with their emotional wounds and their inability to easily connect with the world around them. As they live together, the deep scars carved into Umi heart begin to surface, revealing the full extent of his trauma. Tamao, who has spent years overcome by weakness, grief, and a tendency to merely hang her head and lament, realizes that her passive sorrow is not enough to save Umi. This realization sparks her first determined declaration to change. She resolves to become stronger, not for her own sake alone, but so that she can truly smile and walk forward alongside him.

The narrative arcs progress from the initial encounter and decision to live together, through the daily struggles of their pseudo-family life, and into a deeper journey of mutual healing. The story is set in a quiet Japanese town near the sea, where the sound of the tides serves as a recurring motif marking the fateful change in Tamao life. The series explores themes of found family, recovery from childhood trauma, and the slow, painstaking process of learning to communicate and trust again. The central conflict arises from the collision of their pasts with their fragile present, as both Tamao and Umi must learn to confront their pain directly rather than simply being crushed by it. The narrative follows Tamao growth from a silent, mourning woman into someone capable of fierce, protective love, and Umi parallel journey from a dark-natured, wounded boy toward the possibility of a happier life.