Get them when they're young

They're all vipers, Shizuki had always known it, so she will do what is needful. Her father had wanted a son, but she can do as well as any son, or better.
She's gonna do it the way father taught her: the daggers in the belt of her kimono, poison in the ring on her finger, a piece of string curled around her wrist. You have to get them young, like weeds, before they smother everything that could be good.
Her friends smile when Shizuki comes to lessons next day, but she knows what must be done. They're all vipers.