Emperor ' s Key The Emperor ' s Key ( 皇の鍵 , " Ō no Kagi " ) , sometimes shortened to the Key in both versions and also called the Golden Key in the dub , is a pendant that originated from the Astral World in the " Yu - Gi - Oh ! ZEXAL " series . It is currently in possession of Yuma Tsukumo and he uses it to summon Astral , which is similar to that of when Yugi Muto transforms into Yami Yugi with the power of the Millenium Puzzle ( both items are also similar in that their owners are frequently shown wearing them around their necks , and they have been stolen from their respective owners on one or more accounts , only to be later recovered ) . The Key has an inside world which is the " pocket dimension " , in which Astral spends most of his time . It has the power to subdue the influence of a " Number s " and can open The Door . Features . Appearance . The Key appears as a key with golden curves and a ring on top , allowing it to be worn around the owner ' s neck . It also has a green gem , which contains the " pocket dimension " . Pocket Dimension . Within the Emperor ' s Key is a pocket dimension where Astral spends most of his time . In case the Key is taken from Yuma or Yuma loses it , Astral will be trapped inside this dimension if he is within it . However , that won ' t be the case if he is outside of the Key . The pocket dimension is made up of energy similar to Astral World with floating particles along a white desert covering the whole place and in the air is a huge green airship . Gaining access to this world requires going through The Door . Kite Tenjo was able to get to the pocket dimension by using a Baria Crystal . Different Dimension Airship . In the middle of the pocket dimension is the Different Dimension Airship , where Astral resides . Abilities . The key is very resilient and can even repair itself under certain circumstances . The Emperor ' s Key gives the user some resistance to the influence of the " Numbers " . It has at least once failed to fully suppress the power of a " Chaos Number " , For example : When Yuma took control of " " via " Rivals Unite " , it was causing him great pain until Shark used " Underwater Snow Prison " to banish it from the field . A diabolical door has haunted Yuma in his dreams trying to convince him to open it . The Emperor ' s Key was also the key to open that door , which released both Astral and the " Numbers " ; and to do so , the broken key restored itself . When the Key got separated from Yuma , a voice said that " Astral is immersed in the guidance of time " and that he must obtain the power of " ZEXAL " . The voice described it as a power that turns all darkness into light . The Key has the power to release the alternate form , of a " Number " - " Chaos Number " . The " Numbers " have power inside the Key , as when Astral sent " " off , the Key fired the card out of the Key and into Yuma ' s Extra Deck . Additionally the key has the power to make Astral visible to anyone when it radiates strong energy , such as during Yuma ' s Duel against Fortuno , and when Yuma ' s friends were able to see Astral inside the cockpit of the Different Dimension Airship . Anime history . Pre - series . Kazuma Tsukumo received the Emperor ' s Key from a being similar to Astral . This caused him to see an attack occurring in Astral World . Kazuma later passed the key on to his son , Yuma . Yuma held onto the key as a keepsake of his traveling parents and usually wore it around his neck . He felt that the key opened many possibilities and made him think he could take on any challenge . Despite this , Yuma suffered nightmares about a demonic door , telling him that whoever opened it would receive great power at the cost of a great risk . The key would light up during these dreams . Yu - Gi - Oh ! ZEXAL . One day , Yuma confronted Reginald " Shark " Kastle at school , over him stealing Bronk Stone ' s Deck through an ante . During the encounter , Shark noticed Yuma ' s fondness of the key , so he swiped it . He proceeded to break it in front of Yuma and throw a piece away . Bronk managed to find the piece Shark threw away and later returned it to Yuma . The next day , Yuma confronted Shark in a Duel . Before they began , Yuma held up the piece of the key Bronk returned to him , and as he demonstrated his confidence , the other part of the key was transported from his house to his hand and the key repaired itself . Yuma was transported to the door from his dreams and this time , he inserted the key . The door was unlocked releasing Astral . Yuma then returned to his Duel , with Astral by his side . The granted resistance to " Numbers " when Number 96 tried to take " " from Bronk Stone by force , and when Bronk Summoned " Utopia " . When Shark had the Key and took control of Kite Tenjo ' s " " . However , the Key was unable to fully suppress the power of a " Chaos Number " when Yuma took control of " " . Though the " Chaos Number " did not possess him , the connection to it weakened Yuma and surrounded him in a dark aura which was eventually electrified , causing him great pain . Vetrix pointed out that if Shark did not do something , Yuma would be taken over by the " Number " like he was . World Duel Carnival . The original wielder of Key , Kazuma Tsukumo , also has power over the Key as well . He mysteriously appeared in the Key and used the power of the 12 collected " Numbers " to break Trey ' s influence over Yuma , allowing him to regain his " kattobingu " . Kazuma later returned to tell the revived Astral that his son is calling him for help . Yu - Gi - Oh ! ZEXAL II . When Yuma Dueled against Fender , Astral ( whom was in the key ) was electrocuted at times when Yuma ' s Life Points went down . When Yuma and Ray Dueled against Girag , Yuma threw the key out of the Barian ' s Sphere Field to Tori once Astral was weakened from the effects of the field . After their Duel with Number 96 , Astral was forced to return to Astral World and the key went with him , falling through the portal . Later on after Yuma ' s Duel against Eliphas concluded with the former ' s victory , he returned the key to Yuma . After meeting up with Reginald Kastle after he and Rio Kastle sided with the Seven Barian Emperors , the Emperor ' s Key reacted with Nash ' s Barian Emblem , letting Yuma observe Nash ' s past life while Nash witnessed the events that Yuma had been involved with in Astral World . In the Key ' s pocket dimension , Astral and Kazuma discussed Yuma ' s future and the upcoming ceremonial Duel . Manga history . The Emperor ' s Key fell into the hands of Mirai Tsukumo , who passed it on to her son , Yuma . Although Shark had broke it into 2 pieces , during the Duel between him and Yuma , the key restores itself , and Yuma uses it to open The Door , which releases Astral and the " Number s " .