High-school girl Kamigaya Kai often gets confessions. She then poses a requirement "If you let me stab you to death, I'll give my love to you.". This way people don't reaproach her in her quest to live her boring life, with boring parents, boring school colleagues and boring media.
Kuwashima Kusabi, a seemingly plain girl brightens the world that is "boring" to Kamigaya Kai. It first seemed like she was the 5th confession that turned someone off, but she ran home instead to fetch a sturdier knife.