Baccano

In the year 1711, a group of alchemists are granted an elixir of immortality, with the stipulation that they must kill each other until there can be only one. The now-immortal group unanimously decides it wasn't worth it and destroy the elixir; but one of them, Slizard Quates, starts to kill off his fellow immortals. To reduce the risk of Quates tracking them all down, the group separates and goes their separate ways. Neither of them crosses paths again till 1930....