Hakiri-san wa Kimi dake no Shinigami ni Naritai

Nikami, an ordinary high school student, has no interest in falling in love, let alone getting married. One day when he's leaving for school, the Grim Reaper is standing there, with a giant scythe! Rather than killing Nikami, she introduces herself as Hakiri, and she came form the Underworld to help Nikami die. She claims that he will only die if he gets married! A first in human history. Nikami tells her that he doesn't have a girlfriend, but Hakiri responds with a proposal! A shocking romcom about instant death by marriage!

(Source: Kodansha, translated)