Daikichi Kawachi, Ken'ichi Matsuyama, returns home for his grandfather's funeral and uncovers a surprise that unsettles the family: Rin Kaga, the grandfather's illegitimate six-year-old daughter by an unknown mother. Rin is barely welcomed and quickly treated as an embarrassment by relatives who prefer to keep her at arm’s length. In the face of growing disdain, Daikichi chooses to break with his kin and bring Rin into his life, even though he is single and has no prior experience raising a child. What starts as a bold act of responsibility soon becomes a demanding, often humbling journey as he learns firsthand the many everyday challenges of single parenthood.
Daikichi’s day-to-day life grows more complex as he discovers how to balance work, finances, and care for Rin. He finds guidance and support from the people around him, including a single mother whose son is Koko Nitani. Rin meets Koki Nitani, a boy who becomes a part of her world, and their dynamic helps shape Daikichi’s approach to parenting. Ruiki Sato brings to life Koki Nitani, whose presence in Rin’s life provides practical lessons and moments of connection that soften Daikichi’s initial hesitations. Through trials at home and in the community, Daikichi learns that his sacrifices may be worth it, gradually recognizing the depth of his commitment to Rin.
Across the first year, the narrative centers on Daikichi’s perspective and the emotional and logistical work required to raise Rin. He navigates holidays, school enrollments, health concerns, and the quiet, persistent questions about what family means when bloodlines aren’t the measure of care. The story often feels intimate and grounded, portraying growth, patience, and the evolving bond between guardian and charge.
Ten years pass, and Rin grows into a high school student with her own questions about life, love, and the future. The remainder of the series shifts toward Rin as she grapples with her feelings for Koki Nitani and begins to shape ideas about a future career. A pivotal realization emerges: Rin discovers she is not related to Daikichi by blood. The series culminates with Rin envisioning a future where she and Daikichi might share parenthood, a bold, provocative ending that the anime and live-action adaptations choose not to depict. Instead, both adaptations conclude before the time skip, leaving that revelation unshown on screen.
