Mooyoung is a Dicer and was Taebin's mentor, the person who gave him his first Die. He seems to currently be the most powerful A Ranker. He killed most of all other rankers in Taebin's former school (excluding Taebin and Dawn). His motivations have something to do with the "Last Die" and the connection between him and X but the rest is unknown.
Appearance
Mooyoung is an athletically built youth with brown skin and white hair. He is very tall (even more so than Taebin) and has eyes that are closed or hidden by his hair. He wears a hooded blue jacket with a white under shirt and blue jeans.
Personality
Mooyoung is outwardly affable and charismatic. Initially, he treats Taebin like an apprentice under his wings, and encourages him to evolve as a Dicer to get back at all of his former bullies. Behind that kindness, though, Mooyoung is cold and calculating, and his only ambition seems to be to become the Top Ranker by whatever means. He has fully embraced the implications of the quest system and seemingly has no compassion for other people, being ready to kill them if it helps him to achieve his goals.
History
Mooyoung was a student from Taebin's old school. He first appeared in the story when Taebin was considering suicide as a consequence of the relentless bullying he suffered. Surprising him from behind in the middle of the rain, Mooyoung caused Taebin to almost fall from the building, but he saved him and gave Taebin a Die saying that he died that day and the life he had, now belonged to him.
After that Taebin worked together with Mooyoung learning as much about Dice as he could and often giving his mentor a share of his own earned dice. Mooyoung praised Taebin for realizing the role of desires in the generation of Dice, but implied that desires could never be truly quelled, as they evolve and become more ambitious. Taebin failed to understand the implications, and why Mooyoung gave him Dice in the first place, but Mooyoung didn't elaborate.
Over time Mooyoung assembled a small group of Dicers, apparently much in the manner of the later guilds in Dongtae's school. He kept an aloof position and didn't reveal his thoughts, even to his admirer Taebin. Finally, Mooyoung gathered the members of his group and killed them. He grabbed Taebin and told him that he aimed to attain the next level of Dice, but Taebin escaped at that moment and nothing more was said on the matter. Before Taebin left for good, Mooyoung said running away was futile, because no matter where he went, Dice would eventually spread to other people in that place and the cycle would begin again.
He appeared as a "prophet" for Gilma's guild, giving them a Die that would indicate when the rules would change. Later, he killed the guild and took the A-rank Die that fell. At this time, Mooyoung was co-inhabiting Taebin's body and had temporarily taken control.
By the time X launched the new mass quest in Dongtae's school, pitting A-Rankers against each other, Mooyoung had managed to track Taebin down and reach the school. However, it was later revealed by Taebin that the Mooyoung who had come to the school was not the "real" Mooyoung (it was Dawn in disguise as Mooyoung), as his movements and attack patterns were different.
Powers and Abilities
Mooyoung is currently an A-Ranker (in the timeline of Dongtae's story), but having been a Dicer longer than the other characters in the story, he has evolved beyond everyone else. He seems to have maxed out most of his physical skills. His strength is superhuman, and he has killed other A-Rankers by just crushing their spinal cords from behind with one hand. His endurance is such that even kicks and punches from Taebin are unable to lay a scratch on him.
His trademark skill is Time Pause, like Dongtae's. He uses it effectively to defeat any attempts at resistance from other A-Rankers while killing them. He also seems to be immune to Time Pause cast by Dongtae (which is probably a natural resistance of all Time Pause users). He also currently has access to the Teleportation and Psychokinesis skills, gaining the latter from Gilma and the former via Taebin.
It is heavily implied that Mooyoung has become an S-Ranker multiple times before, but has always failed to beat X.
Relationships
Taebin: Mooyoung ultimately uses his apprentice as nothing more than a tool. Initially he saves him and helps him be reborn, and while at a certain point Taebin suspects that Mooyoung just wanted someone to provide a steady supply of Dice with his desires, the truth is even uglier. In a sense, though, Mooyoung seems to have a certain respect for Taebin, since he was the only person to whom he bothered to explain his own ambitions. It is later revealed that Mooyoung is currently co-inhabiting Taebin's body as an alternate psyche that gradually surfaces as Taebin gains more A-rank skills.[1]