Read manga: Kuro No Shishi

manga
Other name: 黒の獅子 ; Black Lion
Artists: NAGAI Go
Status: completed
Latest chapter: Vol.1 Chapter 3.2
Updated at: Aug 25, 2019
Summary:

One of Go Nagai's first works, this violent period piece takes place in the 1500s and stars a talented low ranking ninja named Shishimaru. In it, Shishimaru fights against Ginnai Doma (an immortal samurai who, despite being butchered multiple times, doesn't die) because Ginnai murdered his comrades. Despite being set in historical times, it has machine guns/lasers/robots/atomic reactors with no real explaination.