Devil King Sword

Devil King Sword ( 魔王剣 Maoken) is currently onimaru's weapon.

Summary
The Devil King Sword is a fiendish weapon of incredible power forged by Kaguya and is the evil counterpart of the Supreme King Sword.

Appearence
It looks like a huge, double-edged longsword with a black blade and white borders. The handle is black and rectangular, and with a white tip. The hilt itself is composed by a round body shaped like a fiendish head (with the open mouth serving as a power gauge) and two horn-shaped arms protunding to the sides and adorned by what seems to be black fur. The blade of the weapon is slightly larger at the bottom and sports a hook near the hilt. This blade can turn the evil spirit of the user into energy blasts capable of erasing all life from the Earth. When fully unleashed the blade turns into black energy.

This means that if the liberated Haoken is a lightsaber the maoken is a darknesssaber and that it can have many more powers in that form based on darkness

in the manga and anime Gekko uses his evil energy to heal his eye and imbue the blade with dark energy to create a huge blade of darkness that could slice everything and also project a dangerous energy field to protect itself as to harm yaiba.

Techniques
According to their power gauge, It has three attack forms:

Used by Onimaru

Used by Gekko