Becoming the "Black Sword of Ultimate Light", it is no longer sheathed in Invisible Air and takes on a different appearance. Rather than creating an almighty slash at the tip of the sword, Excalibur gathers a large amount of prana to cover the sword in a black light with the same shape. It matters not if it is filled with good or stained by evil, as the fact that it is the strongest holy sword does not change. It can either be used to attack as a blazing black flame in a similar fashion to the regular Excalibur or, as shown in Fate/unlimited codes, swung like a sword in an upward arc multiple times as a technique named Vortigern: Hammer of the Vile King.
Due to the corruption and the enormous amount of prana received from Sakura, Saber can fire this version of Excalibur without limit.