Hell’s Paradise: Jigokuraku (webtoon)

Gabimaru, once renowned as the most powerful ninja, finds himself captured after attempting to flee his village. Yamada Asaemon Sagiri, his executioner, offers him a deal: to be exonerated of all crimes by the Shogunate, he must locate the Elixir of Life in Shinsenkyo, a realm rumored to be paradise. The man who claims to be devoid of all human emotions and attachments must now embark on a journey to explore the meaning of life, death, and humanity!!