Excalibur (エクスカリバー, Ekusukaribā?), differentiated from the Excalibur of Fate/stay night as Excalibur Proto: Sword of Promised Victory (約束された勝利の剣, Yakusokusareta Shōri no Ken?) in Hanafuda, is the golden holy sword of King Arthur. Differing from that of Saber's Excalibur, it is a double-sealed weapon locked by two seals, Invisible Air and the Restraints of the Round Table (円卓拘束, Entaku Kōsoku?). The Restraints, the Thirteen Constraints of Camelot (, ?), are conditions set by the Knights of the Round Table that must be met before it can be utilized, including:
- The battle must be an honorable one
- The enemy must be more powerful than yourself
The seal will be released upon over half of the thirteen Restraints being met. The seals remain locked until he activates it, causing a series of clanking sounds as the Restraints are lifted one by one. Activated to counter Enki, it releases as an expanding pillar of light that cleaves both the "star of destruction" and Archer with a single strike. Expanding larger than the city, it can even be witnessed from space. It is a Divine Construct like its counterpart.
Fate/Prototype Tribute Phantasm
"Proto Sabre's Excalibur is locked by two seals, one being Barrier of the Wind King, the other being 'Restraints of the Round Table'. Some examples of the Restraints including:
-The battle must be an honourable one
-The enemy must be more powerful than yourself
The seal will be released if more than half of the thirteen Restraints are passed."