Nanohana Sai, a devoted father to ghostwriter Jiyu Nanohana, channels his guilt over his wife’s death—an event that unfolded while he worked late, leaving Jiyu alone during her mother’s final moments—into relentless dedication as a stay-at-home parent. His jovial, clumsy exterior masks expertise in Yagyu Shinkageryu Mutodori, a non-lethal swordsmanship technique he imparted to Jiyu to safeguard her. Though he ghostwrites samurai dramas, his creative dissatisfaction lingers. When Jiyu prods him to author a romance novel under his name, he briefly capitulates to his former employer’s ghostwriting request, straining their bond.

Sai’s protective instincts drive extreme sacrifices: during a conflict, he permits an adversary to possess his body to shield Jiyu. Yet his vulnerabilities surface when manipulated by Freesia Yagyu, culminating in a slap that triggers Jiyu’s amnesia. This fracture compels him to confront his parental failures, sparking a heartfelt reconciliation and renewed commitment to her well-being.

Unspoken affection for Mikage Tsumura, his married supervisor and a remnant of his past, weaves tension into their interactions. Post-conflict, he collaborates with Mikage professionally, harmonizing writing ambitions with paternal responsibilities. Through guilt, regret, and tentative growth, Sai evolves from a self-reproaching figure into one embracing accountability, supporting Jiyu’s journey while cautiously pursuing his own fulfillment—a man balancing concealed competence, unresolved yearning, and hard-won resolve.