Hitokiri
Hitokiri (人斬) is any one of numerous
samurai in
Japanese history who were amazingly strong and considered undefeatable by normal people. Hitokiri literally means "Person Slayer", but is better translated as
assassin.
One of the most famous Hitokiri was Kawakami Gensai, said to be totally undefeatable. Kawakami Gensai was the character model for Himura Kenshin in the anime Rurouni Kenshin.