Hell's Paradise Jigokuraku Vol. 01

Gabimaru the Hollow is on death row for crimes committed as an assassin when he's made an offer: die in prison, or travel to a mysterious island to locate the elixir of immortality for the shogun. He soon finds himself trapped on an island full of otherworldly creatures, rival criminals and ruthless executioners eager to take the head of any criminal who steps out of line.
For mature audiences.