An amiable samurai who would rather eat than fight. During the Great War he avoided fighting by taking a position as a combat engineer and has since then taken up chopping wood in exchange for food or various devices that interest him. He is most helpful within the group as their mechanic, and orchestrates the construction of medieval-type weapons to fight the giant mechanized Nobuseri. He loves rice more than any other person in the series and can tell where it's from just by the taste. He hates traitors, and is uncompromising in that respect due to the fact that he once betrayed his comrades by revealing information that resulted in his entire platoon being killed. He grows to become a more forgiving and understanding man due to Kambei's influence. The sword he carries has a rain charm hanging from the end.
During the final battle with Ukyo, Heihachi comes up with a plan to stop Ukyo's fortress by separating the engine from the rest of the ship by blowing up the connections. Just as he's finishing setting up his plan, he gets pinned to the ship by a large chunk of metal and is forced to detonate the explosives while he's still on the engine, where he falls to his death. Upon searching the rubble from the crashed engine, Rirara and Komachi discover Heihachi's weather charm.