Telling ghost stories is a favorite past time of Mai Taniyama and her friends--that is, until she meets 17 year-old Kazuya Shibuya, the man sent by Shibuya Psychic Research Center to investigate paranormal activity at a supposedly haunted school. When Mai gets caught in a dangerous situation, she is rescued by Kazuya's assistant. Saving her lands the assistant incapacitated, and Kazuya demands that Mai become his assistant, instead...

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.

In this world, from ancient times, people were eaten by beings called "youma". For a long time, people lived without any means to counter them. However, a half-human, half-youma female warrior was born.... Female soldiers known as "Claymore" who, with silver eyes that can see through to the true form of "youma", and carry a large sword as a weapon, continue to battle those which people have named "youma".