Yukarisu

Serving as a waitress at Mitsuha’s family restaurant, this high school student maintains a secret, deadly life as a professional combatant. While she is romantically involved with the restaurant's manager, her true purpose is to hunt anyone who detects the Shocker organization. When Mitsuha and her companions accidentally uncover the group's existence, she ruthlessly turns against Toujima and his allies, launching a lethal strike to eliminate all witnesses in a single, violent ambush.