Mysterious Heroine X Alter (Fate)'s weapon. It is often seen resembling a red Double Bladed Lightsaber, but originally took a form resembling a glowing red Energy Sword variant of Himitsucalibur (Fate) and by extension Excalibur (Fate/Stay Night) with red markings on its Hilt. It can also transform into a Chainsaw.
Similarly to Himitsucalibur (Fate), if its portrayed in its original form without the glowing element, it may simply be tagged as Excalibur (Fate/Stay Night).