Taiyo Asano is a high school student who lost his entire family in a car crash and has become socially withdrawn, finding solace only in his childhood friend Mutsumi Yozakura. His life is upended when he learns that Mutsumi is the head of the Yozakura family, the world's most powerful clan of spies. Her eldest brother, Kyoichiro, is dangerously overprotective and views Taiyo as a threat, so the only way for Taiyo to survive is to marry Mutsumi and become a member of the family. Thrust into a world of espionage, dangerous missions, and eccentric in-laws, Taiyo begins training to protect Mutsumi and uncover the secrets of his own past.

The setting is a modern world where the Yozakura family operates from a sprawling, heavily fortified mansion filled with deadly traps and advanced spy gadgetry. Each sibling possesses a unique superhuman ability derived from their genetics: Kyoichiro wields near‑invisible steel threads, Futaba is a master martial artist, Shion specializes in intelligence and technology, Shinzo is a charismatic infiltrator, Kengo is a super‑strong child‑like fighter, and Nanao is a genius inventor. Mutsumi herself has no special powers, but as the family head she commands their loyalty, and her potential children are sought after by enemies who wish to prevent the next generation of superhumans.

Notable narrative arcs in the first season include Taiyo’s early missions, such as capturing the bomb‑obsessed criminal Tamaya, which force him to prove his worth as a husband and spy. Later arcs introduce the mysterious first matriarch Tsubomi, who appears in a dream and asks Taiyo to kill her, prompting him to undertake the brutal Silver Spy Examination to gain answers. This exam pits him against ruthless inspectors while the family’s long‑estranged father, Momo, resurfaces with a sinister plan that threatens the Yozakura household. The season culminates in a direct confrontation with Momo and the unraveling of deeper secrets about the family’s past and Taiyo’s own origins. A second season continues the story, delving further into the family’s history and Taiyo’s growth as a spy.