M-21 engages in this battle to prevent Aris & her companions from capturing Shinwoo.
Dr. Aris returns to South Korea without Dr. Crombel's permission to find an experiment specimen. She takes an unhealthy liking to Shinwoo after seeing his fight with multiple delinquents. Yuri and Mark arrive on the scene, and the former tries to stop Aris but gives in to her demands in order to pacify her even though he's clearly aware that they are in hostile area.
Their plan is ruined by the sudden arrival of M-21 who reminds them that they weren't supposed to be in this area. M-21 provokes them enough to engage in a battle.
They change the location to an isolated place where they can fight without restraint. Dr. Aris decides to teach the "trash" agent a lesson. She changes into her nano suit and launches an energy blast on M-21. The beam finds its mark as M-21 takes on the direct hit. Aris, Mark and Yuri believe that the attack was too strong and has most likely killed M-21. However, the smoke clears and they are shocked to see M-21 in his 'more evolved' werewolf form.
Dr. Aris is furious at the transformation of a confirmed 'failed experiment' and launches her energy whip on him. M-21 grabs hold of the whip and uses it to pull her towards him. He punches her in the guts and she falls drops down unconscious. It's a single-hit victory.
After Aris is down, Yuri launches a powerful energy beam which M-21 blocks with his hand. Yuri is shocked to see such strength from a failed experiment. Before he could think further, M-21 is already on him and launches a frontal attack which leaves him unconscious.
Mark, now left alone, is visibly scared of the power displayed by M-21. Before he could act, M-21 is behind him and asks him why is he still pretending to be M-24. Mark aims a punch at him but M-21 doesn't even need to dodge. He grabs hold of Mark's fist and lifts him up by his throat. M-21 then trashes Mark for offending the memory of his treasured friend.
M-21 defeats his opponents with relative ease. Aris gains consciousness and expresses her envy at M-21 for getting such wonderful power. It irritates M-21 to hear such things from someone who doesn't know the pain they, the experimentees, had to go through even though they did not want such power. M-21 is ready to kill her when Muzaka appears. Tao and Takeo enter the scene as well and both parties come to an understanding, ending the fight.