Mission: Yozakura Family, Vol. 1 by Hitsuji Gondaira

Romance! A crazy, overprotective brother! And...spies?

Taiyo Asano has been on his own ever since his parents died and the only one who seems to care for him is his childhood friend and classmate, Mutsumi Yozakura. But Mutsumi has a secret–she is the head of a family of spies! And on top of that, her brother Kyoichiro is dangerously protective of her! To stop Kyoichiro from killing him, Taiyo and Mutsumi must take the ultimate leap–marriage! Because in the Yozakura family, family cannot kill family.

Taiyo Asano is a super-shy high school student and the only person he can talk to is his childhood friend Mutsumi Yozakura. However, Mutsumi comes from a line of master spies with amazing powers. Her oldest brother, Kyoichiro, is obsessed with Mutsumi and out to kill anyone who gets remotely near her—and his next target is Taiyo! The only way for Taiyo to save himself from Kyoichiro’s murderous clutches is to marry Mutsumi!