There was this girl who always wanted to die and then she met two guys who were reapers. She started seeing black ribbons around other people's necks and they explained to her that was a death mark or something like that.
Then she got one around her neck and she realised that she didn't want to die anymore.
This is Zombie Loan.
Michiru Kita possesses the Shinigami Eyes, a power which allows her to see a person's closeness to death by seeing a ring around the person's neck. When a person is marked to die, a gray ring appears, which darkens over time. Once the ring turns pitch black, the person dies. Chika Akatsuki and Shito Tachibana, two boys in her class, both have black rings around their necks, but are still alive. It is revealed that after an accident that was supposed to kill them both, the two made a deal with Zombie-Loan. In return for keeping them alive, the two have to hunt zombies to pay back their debt.
The manga you are looking for is called "The Deathless"
Synopsis" -An ordinary girl as she is, she possesses the eyes of death which can make her see the death rate of others. Even if she's troubled, she has no access to death! Hearing her calling, the god of death comes for her. However, it’s useless? What will happen between a girl who desires death and the god of death who cannot kill the girl? What’s the secret of the girl's super power... Endless Twilight
