Shark (Kor. 샤크) was a Modified Human who worked for the Union as a member of the DA-5, a special forces team of the Union that was created by Dr. Aris and led by Krantz. His life ended when he was absorbed by Krantz.
He is a brutal and heartless bully. He loves to kill people for his own amusement and takes any opportunity to do so. He is extremely haughty in nature and is also easily provoked. His bloodthirsty, sadistic nature has made him detestable to other members like Tao and Takeo.
Shark had been sadistic in his ways all along. It is revealed later in the fight with DA-5 members against the protagonists that he killed all the people that Takeo made contact with in their prior missions and that his actions were sanctioned by Krantz.
Shark debuts in a mission at the ranges with his team, where his assault on the opponents turned out to be too 'boring' for him. He let on of them escape to make it an interesting hunt but gets scolded by Krantz who lets Takeo snipe the runaway captive instead (much to Shark's dismay). Later they get another mission: to investigate Dr. Crombel's doings in Korea and reach the base of action.
Shark takes a stroll around the city and notices Takeo who has met the children. He meets Takeo and irritates him by asking if the kids reminded him of his sister.
Later Shark and Hammer corners M-21 and ask him to come along with them but he refuses. Shark tries to intimidate M-21 by releasing his aura but has to stop when Regis and Seira arrive at the scene. Shark engages in a clash with Regis (no match for the young noble though) despite M-21 warning Shark that they are nobles and Union is supposed to be in a sort of treaty not to fight with them. Krantz intervenes and takes M-21 with them while Regis is left with a misconception that M-21 might have been working for his mission all the while and Shark with a desire for revenge against Regis. For the time being, he sustains himself with beating up M-21 during interrogation.
Shark then finds Tao meeting up with Ikhan and when alone with Tao, he reveals that he has been killing every single human Takeo met during past missions, just because he doesn't like Takeo. But he sarcastically tells Tao that he won't do so to the boy Tao has met as he does not have any enmity with Tao.
Shark spends his later days beating up M-21 for interrogation and constantly irritated at Krantz' order to keep it low. Getting some free time, Shark wonders what they should do to kill it and decides to go find the kids (Shinwoo and Yuna) who Takeo previously met with. Hammer accompanies him. They find the children and Shark is surprised to see that kids who met Takeo and the one who met with Tao are friends. Both of them are even more excited to see Regis with them.
Shark and Hammer meet Regis in an isolated area, having put a boundary around them to prevent interference. Shark tries to provoke Regis but turns out to be the one provoked instead. Shark gets furious and attacks but Regis easily stops his attack, forcing Shark to retreat backwards. Their one-on-one fight proves Shark clearly outmatched and Hammer intervenes to save him from Regis. Although reluctant, Shark is convinced to retreat by Hammer and they return to their base, defeated.
Shark gets a chance to avenge his humiliation by facing off Regis once more, this time imbibing D for enhancement. He manages to cancel out Regis' mind control but unknown to him, his opponent has been holding back misunderstanding him to be M-21's friend. When that clears up, Regis takes control of the fight. Just as Shark is about to receive a finishing blow from Regis, Hammer arrives with unconscious children. Seeing Regis stop fighting, Shark is surprised, elated and ties up Regis with special handcuffs. He hits Regis unconscious and they take Regis and the children to their base.
At the base, Shark shows all other members their success in capturing the witnesses. He also reveals in front of Takeo how he has been erasing the existence of all people Takeo had met and with Krantz' authorization. Then Shark entertains himself with the children who have woke up. To his surprise, they appear to be acquainted with M-21 who affirms that they are no more than just acquaintances. At this, Shark decides to kill the children then and there. Shark hits Shinwoo who receives the blows but stands up again and again for his friends. Finally, M-21 attacks Shark using his transformation to save the children.
Shark attacks M-21 like a fanatic while M-21's transformation gradually reaches its limit and he turns to normal. Shark aims a fatal blow and M-21 faces it head on to shield the children and collapses, bleeding profusely. Regis gets up and takes over the battle from M-21. Shark takes his D and transforms but is no match to Regis. When Regis is about to finish off Shark, he is stopped by Krantz who orders Shark to step away and berates him for being so weak.
Shark, infuriated for his humiliation plans to attack the children while Regis and Krantz continue their battle. However, M-21 manages to stand up against him but Shark easily stabs him with his blade.
An intruder alert breaks out and Rai appears faster than Tao's estimated time, surprising everyone (except M-21). Shark gets annoyed as he asks hoards of questions to the newcomer who does not make a single reply. Suddenly, Krantz, Shark and Tao become immobile. Rai reveals it's the power of his mind control as he has not permitted them to move. Shark suddenly clutches his own throat and falls to his knees in front of Rai who turns to Shark and says: "Neither did I give you permission to breathe."
The mind control is broken by Krantz who commands Shark to take D. Shark obliges and then, to everyone's surprise, he is absorbed by Krantz. His drained corpse is subsequently obliterated by Blood Field along with Krantz.