Baccano!

Summary: 

    In 1711, a group of alchemists seeking eternal life gathered on a boat to summon the "demon" that held the secret. The demon agreed to give them what they wanted—an elixir of life, the method to create more, and the secret to ending their new-found existence. The following night, alchemists began disappearing, "eaten" by one of their own. Realizing the threat posed by being close together, they decided to scatter across the world.

Centuries later, in Prohibition-era America, the immortals have come together once again, and the "stupid commotion" starts.