Ano Hito ga Kieta

Set in an apartment building where many people are rumored to disappear one after another, the story begins when Maruko, a young delivery worker, accidentally discovers the secret of a suspicious resident. He and his older colleague Arakawa, who is an aspiring novelist, try to discover the resident's true identity. But in the end, the two got into an unexpected big incident. (Source: Japanese = natalie.mu || Translation = MyDramaList)