Demon City Shinjuku is a novel written by Hideyuki Kikuchi that was also adapted into an OVA. The "Demon City" refers to Shinjuku after a powerful wizard, Levi Ra, utilizes an evil magical sword to seperate the city from the rest of the world. Ten years after this a teenager, Kyoya, is drawn into the city to protect the president's daughter as well as finish a fight that his father started. He meets up with two of Levi's demonic underlings, and a third is tracking him before she decides to fight with Mephisto, a resident of the city, instead.
The demon can easily take a human form, but it can also take the form of a shadow as well as transform her limbs into prehensive tentacles. She can regrow these tentacles at will, and finally also has sulfuric acid as a body fluid. This last ability turns out to be her downfall, as Mephisto stuffs an open bottle of beer into her mouth. The chemical reaction of water and acid detonates her body and takes out most of the building too.