Hell's Paradise: Jigokuraku, Vol. 1

Even an invincible ninja may not be able to survive Hell's Paradise!

The manga series is set in the Edo period in Japan with a Shogun sending a bunch of criminals sentenced to death to a long hidden island to find the elixir of eternal life. The first criminal to find the elixir is to be pardoned by the Shogun. Each criminal is assigned a chaperone, which is someone from the Asaemon Yamada clan that's specialized in executing criminals by decapitation. One wrong move = instant death. Once they arrive at the island, it becomes clear rather quickly as to why the Shogun's samurai haven't returned.