Cycle Soul Apartment(たとえ世界が終わっても)

When Miyata is diagnosed with terminal cancer, she decides to join a mass suicide pact with the members of a suicide website. However, the plan ends in failure when only the man that planned the whole thing ends up dying. The owner of the suicide site promises to give Miyata a special poison that will kill her without any suffering, but in exchange he wants her to marry a resident of the apartment he manages.