Grandark is one of three legendary Demon weapons and can only be wielded by Zero Zephyrum.
Zero uses Grandark both offensively and defensively. Grandark's abilities include striking with deadly firepower, extending the blade, blocking and reflecting projectiles, project thorns, absorb the energies of other beings, produce elemental spheres, increase Zero's potential, transform, and fire wave energy. However, due to Grandark's immense power, it also hinders Zero's mobility in the process.
The blade was created and infused with essence by Oz Pone Max Reinhardt as an attempt to counter Duel's Eclipse. There is a soul embedded within the blade. However, the ego refused to let his creator or anyone else wield him, as they were deemed "weak". After a long time, Oz artificially created a stronger body, Zero, whom Grandark accepted as his wielder.
- According to an interview, it is said that Grandark's ego is "strong enough to bring Ancients down to their knees".
- Along with Eclipse, Grandark possesses a humanoid form that appears as a male. The purpose of this form has yet to be revealed.
- It is said that Duel who already has two of the legendary Demon weapons also wants Grandark.