The Wunderkinder Project (1970s): The chemical runoff at the dump was not a random anomaly. In the 1970s, Dr. Ha Won-do, Kim Jeon-bok (Chae-ni's grandmother), and Choi Yeong-jun ran illegal human experiments on 72 children to synthesize an immortality serum. The surviving test subjects developed dangerous powers and became known as 'Wunderkinder.'
The Child of Eternity & Chae-ni's Heart: One test subject possessed a regenerative heart, earning him the title 'Child of Eternity.' After a laboratory fire left the boy brain-dead, Chae-ni’s grandmother secretly transplanted the boy's regenerative heart into young Chae-ni to save her from terminal heart disease. This transplant is the true source of Chae-ni’s immortality and teleportation.
Un-jeong's Secret Past: Un-jeong is not just a civil servant; he was one of the original child test subjects who accidentally caused the 1970s lab explosion using his awakening telekinesis while trying to save his friend.
Climactic Resolution: The Church of Eternal Salvation attempts to launch a chemical blimp over Haeseong City to trigger mass mutations. The squad defeats the cult leaders and stops the blimp. In the post-credits, Dr. Ha Won-do awakens under the rubble, alive due to the synthesized serum.