Zombie-Loan

Michiru Kita has the ability to see a "ring of death" on people's necks, indicating their proximity to death. The darker the ring, the closer they are to dying. Two students, Chika Akatsuki and Shito Tachibana, have completely black rings, which leads Michiru to discover their secret: they're being kept alive by a contract with Zombie-Loan, a loan office that lends out undead workers. In exchange for their extended lives, Chika and Shito must hunt down and kill zombies to pay off their debt.