An unusually long bladed Ninjato, this weapon is made with a special compound that allows its blade to avoid light reflection, thus rendering itself invisible to the human eye.
It was a payment from a Japanese client after the Bolverk Squad performed a mission for him. It's uncommon length allows the user to execute mortal blows and with certain advantage, although extensive training is required to get used to the blade's reach.
The sword seems to be incredibly sharp and durable, able to withstand multiple high-caliber rounds and slicing and piercing human flesh easily; However, the weapon is not effective against armored units.
Xero uses Hollow for the first time in the third chapter of the first Xionic Madness. After Bolverk Squad manages to eliminate all security in the entry hall, Xero employs Hollow for the first time after three Bio Int. Black Ops protected by an energy shield corner both Omega and himself.
Xero is able to deflect the incomming bullets using Hollow and Slicer, and then proceeds to charge and eliminate the enemy soldiers. After overcoming that obstacle, Xero uses Hollow once more to eliminate more soldiers in an outdoors area.
However, the weapon proves to be ineffective against armored enemies: after the ATD appears at the scene, both Hollow and Slicer end up shattering after Xero tries to pierce the tank's armor.