Skyhigh manga

Skyhigh summary:

A serial-murderer is on the loose who just so happens to also be removing the hearts of his victims and taking them with him. His victims however, are not merely random humans as thought by the police. They are in fact, the past and present guardians of the gateway of the afterlife. On the day he is to be married, Detective Kanzaki, who happens to be on the case, discovers that his fiancé Mina has been murdered with her heart also missing. He also learns that the killers are Kudo, a geneticist, and his evil secretary Rei. The two are trying to obtain six hearts from the guardians so that they may call forth a horde of demons from the Gate of Rage and have their every desire granted. Only problem is, once they open the gate the entire world will be covered in darkness. Meanwhile, in the afterlife, Mina encounters Izuko, the Guardian of the Gate. Izuko gives her three options: Mina can choose to ascend to heaven and be reborn, she can choose to forever walk the earth as a ghost or she can choose to curse one of the living to death and as a result be cursed to descend to hell. Mina has 12 days to make her choice. - Wikipedia.