The Ultimate Blade is a legendary weapon and artefact of the Land of Light, passed down for generations through the family of Mother of Ultra. It played a crucial role in the final battle of the Ultimate Wars.
History
On the final day of the Ultimate Wars, Ken and Ultraman Belial descended to the surface of the Land of Light to find Marie, lying injured on the ground, and Alien Empera a short distance away. After helping Marie up, Ken and Belial charged Empera, but were unable to injure the powerful alien. Marie then presented Ken with the Ultimate Blade, a legendary weapon that had been bestowed upon her by the previous generation of her family, and told him to wield it against Empera.
Empera and Ken proceeded to duel with the weapons, Empera taking up his Empera Blade against the Ultimate Blade. In a climactic final strike, both the Ultra and the Alien struck at each other with their weapons; though Ken suffered a wound to his abdomen, the scar of which remains to this day, Empera's injuries were more substantial, and, bleeding particles of light, Empera vanished.
Having witnessed this event in person, the seeds of jealousy were sown in Belial's mind, ultimately setting off a chain of events that would end in banishment after he attempted to steal the Plasma Spark.