The Thunder-Cutter is an ancient and powerful Nihonto used by Hachiman.
The mighty sword's power rivals the Sword of Omens. It is capable of slicing through stone, as well as being able to lead Hachiman in the direction he needs to go. The sword refused to draw when Hachiman tried to attack Lion-O, presumably because the duel was unjust.
In the episode, "Hachiman's Honor", the Automaton was able to wield the Thunder-Cutter, because he was neither good nor evil so the sword was unable to determine who was good and who was evil, and was only able to fight, until Hachiman touched the sword.
- The Thunder-Cutter, based on it's length, is likely a Tachi as opposed to an Uchigatana
- Despite slinging it through his obi edge-up, the sword has proper Tachi-mounting on the saya to be worn edge-down during mounted assault