|First encounter with Dice, as a child|
|Skill||Control of entire Dice System|
X is the main antagonist of the series. He is a supernatural entity who controls the production and distribution of Dice and sets the quests Dicers must complete in order to gather them. He also sets and changes the rules of the game as a whole. His goal, if any, is not known as of now. He calls himself the Game Master (GM).
X is the first character who appears in the series: the prologue is about him. In it, he appears as a scrawny boy with longish, dark brown hair and greyish-blue eyes, wearing oversized clothes and shoes and with the body covered with bruises.
After becoming the GM, he has only been seen in partial glimpses half-obscured by darkness, but it seems he hasn't changed in appearance since that time.
In the prologue, X origin is shown. He used to be a boy living in a slum in South Korea, physically abused by his alcoholic father and apparently motherless. One night, while trying to escape another vicious beating by his father, he runs out of his house and stops to look at the sky while scorning the idea of wishing upon stars.
At that moment, he is found by his father, who intends to resume the beating, but before he has the chance what appears to be a meteor hits the area and the impact causes him to release the boy. X rushes to the impact site and is stunned by seeing himself before a huge pile of blue Dice of all sizes.
An unknown period of time later, he is already the GM and watches silently as Mooyoung annihilates Taebin's group of friends in the PVP stage. In the events, the reader learns that X lives in a space that can be glimpsed through the smartphones Dicers use, and which has the shape of a giant cube.
When Taebin runs away and tries to start anew in Dongtae's school, X initially just observes the situation but soon understands the circumstances involving the bread shuttle and Eunju, and slowly begins to pull strings.
One afternoon, he notices Dongtae is stalking Taebin and Eunju, and seizes the opportunity to give Taebin a quest that involves sending a Die to the place where Dongtae is hidden. The plan works and Dongtae becomes a Dicer. It is later implied that X always tries to find a way to let Dice spread, even if a user like Taebin is against it and tries to prevent this outcome at all costs.
X tells Dongtae about Dicership and eventually convinces him to use Dice to pursue his desires. In the next few days, Dongtae improves his looks significantly by fulfilling simple and innocent quests, but balks and feels bad afterwards when X makes him lie to a random girl.
In the weeks that follow, Dongtae keeps improving himself by fulfilling non-harmful quests like pranks and chores, but things begin to spiral out of control when he gives a Die to Byungchul.
X initially treats Byungchul like any Dicer, but when he notices the student is trying to hack into the game server to find information about X and Dicership, he decides to take him out. X then gives Byungchul a series of quests that in the end cause him to fall to his death from the fifth floor of the school building. This causes all the Dice he had been carrying with himself to spread over the school grounds, and in the next morning the outcome Taebin wanted to avoid, and which is implied to have happened in the past, comes to pass: the Dice spread to all the students. A period of chaos ensues in which students start harming each other in pursuit of quests, much to X's amusement as he later reveals.
This puts him and Eunju on a collision course. During a quest to save her, Dice meant for Taebin and Dongtae materialise in the presence of Eunju. The two deny knowing about Dice and Eunju, ill-disposed towards the whole idea by the recent events in the school and the explanation on what Dice are given to her by Gilma, declares she will never use Dice and that she will keep those safe by herself.
Seeing his game turned down causes X to snap and he turns Eunju into a target for the whole school, also using the opportunity to give Dongtae his A-Rank Quest by defending her. During the quest, he uses Gilma to meet Eunju for a conversation directly to pry into her reasons for rejecting Dice. Eunju also uses the opportunity to ask him questions, but in the end neither supplies information to the other or budge from their positions, although X is surprised and intrigued by Eunju's questions of whether Dice can be used to change others. He ends up raising the prize on her, but Dongtae and Taebin succeeding in protecting her from the other Dicers.
Not long after, as Dicers begin to fulfill their desires and Quests become more scarce, X begins to raise the stakes, first by launching the Mutual Aggression Quest, which is barely contained by Dongtae; and finally by starting another PVP stage when the number of A-Rankers reaches sixteen. At that point he announces to them that the Final Die can change the world.
When Eunju witnesses a PVP battle between Miju and Sungchul, X uses the opportunity to make another attempt at luring her into Dicership by telling her that her desire to rid the world of Dice is so acute that if she became a Dicer, she would be the strongest of them all. She doesn't bite the bait, and at that point declares she will stop him no matter what. Rather than dismissing it, X seems to take it seriously and retorts that he won't allow her to stand in his way.
When Miju dies, Eunju collects her Cloaking Die but doesn't roll it. X teases her about it but nevertheless begins to treat her as its rightful owner, and from that point on he begins to send her the same notifications he sends to all A-Rankers, including those pertaining the War Quest.
When Eunju realises that the War Quest would not have happened if no one had chosen the Defence team, he is impressed by her insight and decides to try once more to lure her into becoming a Dicer. This time, she is much more vulnerable as a consequence of the events she has witnessed and how things are spiralling out of control, and wavers quite considerably. X even discloses the third target to her in advance as bait, but Mio reminds Eunju of her ideals and she, at least for the time being, refuses once again.
Most of the time, X is cheerful and flippant even when his interlocutors are under great distress. His approach towards all events is to consider them part of the game, and is at his happiest when they are fun. He likes taunting Dicers in general, and even more so those who are conflicted about their own actions and Dicership itself, like Dongtae. He shows total disregard for human life and sometimes his dismissive, careless behaviour verges on the childish.
However, he is very cunning and a great reader of emotions and mindsets. He chooses quests that suit the personality of each Dicer perfectly, and is a master of smooth talk who can word quests so as to overcome moral objections of his targets. He introduces gradations in quests so that Dicers will start off doing innocent things but slowly enter morally grey territory, and only a few Dicers like Mio, Dongtae and Taebin seem to have been able to resist his enticement.
He is seldom discomfited or upset, and indeed the only person who has ever ticked him off is Eunju. He is intrigued by her and has spent longer periods in conversation with her than with almost anyone else.
Despite imbuing most quests with some degree of malice, X is a "fair" GM in that so far he hasn't cheated or walked back in his words. He follows the rules he sets to the letter.
He dislikes adults, and tells teacher Kim he considers them boring due to their obsession with money and drinking. He is interested in how Kim will fare as a Dicer, though.
X has incredible power at his command. He produces and distributes Dice and Quests, and can sense the surroundings of any Die or Dicer's mobile phone in detail. He can also hijack any communication system to convey his words. The A-Rank skills he distributes violate laws of nature. There is also no indication that X has normal human needs like nourishment or sleep. He also seems to be ageless.
Even so, X seems to be somewhat constrained by the rules of the Game. He appears unable to distribute Dice to people who are not moved by desires, for example.
According to Mooyoung, X is the current holder of the S-Rank Die, but whether this means he is the S-Ranker himself is not clear.
Dongtae: X seems to like Dongtae or at least finds him interesting. In the beginning, they were in rather friendly terms at least until Byungchul died. X teases Dongtae often but this has been met with contempt in more recent times, as Dongtae became aware of the noxious influence X exerts over Dicers.
Taebin: X teases him about his attempts to break out of the loop of Dice spread followed by mayhem, which Taebin doesn't like. The two are not seen in conversation often.
Mooyoung: X is very aware of Mooyoung's goal to defeat him but doesn't seem in the least worried about it, having defeated him at least once before. X even tells him he is waiting for Mooyoung to challenge him for the S-Rank Die again.
Eunju: X is very annoyed about her adamant refusal to use Dice and intrigued by the reasons behind it. This has led to diverging forms of interaction with the girl: at the same time he uses every opportunity to put her in danger or in difficult situations, he gives her privileged information others have to figure out for themselves (like the fact that Dice are fueled by desire). He also seems to regard her as a true enemy. She is the only person who has made him lose his composure.