"Legendary Number", pluralized as "Legendary Numbers" in the Japanese version, are a sub-series of the "Number" cards which are unique located in Number's Ruins across the world, protected by guardians. They play an major part of the Legendary Number War arc of Yu-Gi-Oh! ZEXAL. So far, each one of these cards has been based on figures from history (at least history as the canon portrays it).
Legendary Numbers are part of original 100 "Number" cards, but unique. Each of these "Numbers" correspond to a legend inscribed on the walls of the ruins, telling the story of the person who occupied that location in a previous era, before they became ruins due to the ravages of time. Mach, for example, was a Pegasus who served a legendary hero. Three knights who lived in his land attempted to usurp the King, but were intercepted by Mach and his master. Since the hero was unwilling to kill his former comrades, both master and steed were eventually defeated and killed. However, the hero's fellow knights regretted their actions and they buried him and Mach together. Mach later became the "Legendary Number" spirit guardian of "Number 44: Sky Pegasus"
In Yu-Gi-Oh! ZEXAL, the "Legendary Numbers" are unique Numbers whose cards were used by Astral eons ago to seal Don Thousand in the Barian World's Sea of Ill Intent. If Astral obtains them all, he will discover the location of the Numeron Code. However, if the Barian deity Don Thousand obtains them all, he will be fully revived.
When Vector released Don Thousand, Thousand revealed that in order to fully revive him, Vector must collect these seven "Legendary Number" cards. Later, Vector convinced Misael and Durbe to take part in this quest, with the assistance of Mr. Heartland, who is now an insect. Also, Yuma Tsukumo and Astral resolved to take the "Legendary Numbers" after receiving a message from the former's father. In the first of the ruins, Yuma obtained the first "Legendary Number", "Number 44: Sky Pegasus", from Mach. Next, "Dark Mist" acquired the second "Legendary Number", "Number 65: Judge Buster the Adjudicutting Djinn" from Battle Ox.
Seven Legendary "Numbers" have been confirmed with 5 of those "Numbers" being seen so far.
|#||Monster||Sealed Form||Guardian||Number location||Owner(s)|
|Sky Pegasus||Mach||Right shoulder plate||Yuma/Astral|
|Lion Heart||Number 54's guardian||Left side of chest|| Alit (EP: 103)|
Nistro (given by Alit)
|???||Unknown||Number 64's Guardian||Frontpiece of Helmet||Gilag|
|Judge Buster the Adjudicutting Djinn||Battle Ox||Right side of chest||Number 96|
|73||Abyss Splash the Roaring Waterfall Deity||Unknown||None||Unknown||Abyss|