Upon attending his grandfather's funeral, Daikichi, who is thirty years of age, is taken aback to learn that his late paternal figure had sired a child with a younger lady without tying the knot. This information leaves his household dumbfounded and embarrassed, leading them to decline accountability for the reclusive and timid girl, identified as Rin Kaga. Annoyed by this predicament, Daikichi chooses to become her protector. As he raises Rin, he obtains a greater understanding of the highs and lows of parenting.