Shinigami-sama ni Saigo no Onegai wo

Aida Shizuka is three days from being executed for cruelly murdering his family when a shinigami comes to visit him. It's his little sister Hibiki, who has come to make sure his soul goes to hell! Hibiki has another job on this trip as well, granting the final wish of a girl with heart disease, and she drags her condemned brother along with her. Soon, it becomes apparent that people are not as simple as they may seem, and even Shizuka's guilt is uncertain. Hibiki and Shizuka promise to search together for the truth about their family's death, and they won't let life, death, or trouble in the afterlife get in their way!

(Source: MangaHelpers)