Reversibleman

Bizarre corpses are being found at various locations in the city. These bodies look like their skin has been turned inside out. Various rumors and legends arise. Some say these deaths were caused by an infection, while others believe the mafia has their own black market for human organs. The only one that knows the truth is a school girl, who has the ability to store machine guns inside her body! Her name is Luna, and she is determined to seek revenge for her sister's brutal murder by the perpetrators of these "reversing" incidents.

(Source: MangaHelpers)