Meet Louise, a budding magician. The students at the Tristein Academy call her "Zero Louise", due to her current record of zero successes with magic. In fact, her magic tends to go spectacularly wrong. Now, as an important test of her aptitude for magic, she must summon a familiar to be her servant. At this critical moment, she summons up all her magic and wishes for a familiar that is "devoted, beautiful and powerful", and gets... Hiraga Saito, an ordinary Japanese boy. It's difficult to say who is more surprised and dismayed, but the rules don't allow for second attempts. Louise is stuck with her strange familiar, and he with her.

When a human is marked to die, a faint gray line that is invisible to most appears around their neck. As time passes, that ring becomes darker and darker, until it is eventually black, and that person dies. Kita Michiru has an unusual gift, she posses "Shinigami eyes," which allow her to see these rings. When Michiru notices that two of the boys in her Class, Akatsuki Chika and Tachibana Shito not only have rings, but that they're jet black, they reveal to her that they were supposed to die in a tragic accident six months ago. With the help of the Zombie Loan loan office, they were given a second chance at life, they be able to pay for their debt by doing the work of Shinigami and killing malicious zombies. They ask Michiru to assist them with their work. As the story progresses, she finds her everyday life changing dramatically.