A family far from ordinary?! High schooler Taiyo Asano, the 'Ultimate Introvert', lost his family in a tragic accident. The only one he could speak to is his childhood friend, Mutsumi Yozakura who harbors a wild secret as the heir to a spy lineage. Her brother, Kyoichiro, a skilled spy, targets Taiyo. To save themselves, Taiyo agrees to marry Mutsumi and join the Yozakura family, embarking on an unprecedented mission!