Snake Eyes Saburota

 Initially a carefree Ronin who rooms with Hyakkimaru and Dororo at one night, Saburota wants to join Daigo for some unexplained reason. He is later revealed to be a minion of the Fiends and works for them to earn himself a heart.

As a Fiend
He is fought in Chapter 7: Tragedy. You do not receive a body part for killing him as he is not, strictly speaking, a Fiend.

Description
Created by the Fiends to defeat Hyakkimaru, he has no heart, and cannot travel in areas the Fiends do not control. In areas they do control, he has absolute power.