Baccano!

Aboard the ship Advenna Avis in 1711, a group of alchemists summon a demon in the hopes of gaining eternal life. The demon gives them an elixir of immortality and the method of ending their existence, by "devouring" one another, and grants the summoner Maiza Avaro the formula of the elixir. Maiza and most of the alchemists decide that no one else must become immortal; only Szilard Quates opposes. The next night, the alchemists begin to disappear, devoured by Szilard. Realizing the threat posed by staying together, they scatter across the globe.