Relax, I'm a Ninja Series by Natalie Whipple

A Clan of ninjas in San Francisco may sound improbable—but as the son of a ninja master, Tosh Ito knows what lurks in the shadows of his city. Or at least he thought he did. When a killer with a poisoned blade starts cutting down teens, Tosh enlists Amy Sato—newest ninja recruit and his best friend’s crush—and sets out to uncover the killer’s identity. What they find is ninjutsu more evil than they could have ever imagined... moreA Clan of ninjas in San Francisco may sound improbable—but as the son of a ninja master, Tosh Ito knows what lurks in the shadows of his city. Or at least he thought he did. When a killer with a poisoned blade starts cutting down teens, Tosh enlists Amy Sato—newest ninja recruit and his best friend’s crush—and sets out to uncover the killer’s identity. What they find is ninjutsu more evil than they could have ever imagined. As Amy and Tosh grow closer, they discover their connection unleashes a legendary power that could stop the murders. Problem is, that power may be exactly what the killer is looking for, and wielding it could cost them both their souls. less