It's about Akaza and one day she met a man that wanted her to sing for him. Because of an ad at his company and the ad is about Mermaid.
It's about Hell girl or Ai Enma. And her customers is those who seek for revenge because they or someone got treated unfairly in their opinion. In midnight they go in a site called Hell Correspondence and write who they want to send to hell but they will also dig a double grave. And that means that the one who wants to send someone will also be sent to hell after they have died.
This manga was so cuute..
Retake!