Years have passed since Yunagimoto Yuusuke dismissed a childhood vow made by a younger relative as nothing more than innocent, forgotten sentiment—the kind of promise no one ever expects to honor. His solitary life takes an unexpected turn when she unexpectedly arrives at his apartment, now grown and ready to hold him to that long-ago declaration. Confronted with her earnest insistence that he fulfill his youthful commitment, Yuusuke finds himself caught between the weight of nostalgia and the reality of a situation he never imagined would come to pass. What began as a distant memory transforms into an immediate and decidedly complicated proposition.