The trio eventually found themselves back in Seongjin City, the place where all their nightmares began. They settled into Moon-young’s "Cursed Castle," an overgrown mansion that smelled of dust and repressed memories. It was an unlikely, volatile domesticity. Sang-tae, a fan of Moon-young’s dark tales, began to illustrate for her, finding a sense of agency he’d never been allowed. Kang-tae, forced to confront the woman who refused to let him hide, began to feel the cracks in his stoic mask.
A celebrated children’s book author with a penchant for sharp knives and even sharper words, Moon-young was a force of nature. She suffered from an antisocial personality disorder, a result of a childhood spent in a literal castle, raised by a mother who treated her like a "flawless work of art" rather than a human being. When their paths crossed at a book signing, Moon-young didn't see a saintly caregiver; she saw a man whose eyes were as cold and lonely as hers. She decided she wanted him. The trio eventually found themselves back in Seongjin
In the end, the three of them didn't find a "happily ever after" that was perfect. They found one that was real. They piled into a camper van, driving away from the castle, realizing that while it’s okay to not be okay, it’s even better to be together. Sang-tae, a fan of Moon-young’s dark tales, began
The healing was messy. It involved screaming matches, hospital brawls, and the slow, agonizing process of unlearning the lie that they were "broken." They discovered that Moon-young’s mother, long thought dead, was the one who had murdered the brothers' mother—a revelation that threatened to shatter their fragile new family. She suffered from an antisocial personality disorder, a
"You're not a safety pin," she told him, her voice like velvet and gravel. "You’re a bomb waiting to go off."
But the "butterfly" that Sang-tae feared turned out not to be a monster, but a symbol of metamorphosis. In the final confrontation, they didn't win through violence, but through the realization that they were no longer defined by their pasts. Sang-tae realized he wasn't someone who needed to be protected, but someone who could protect others. Moon-young learned that she wasn't a "monster" destined for solitude, and Kang-tae finally allowed himself to cry—and then, to be happy.
Moon Kang-tae lived his life in the shadows of a ghost. As a caregiver in psychiatric wards, he moved from town to town every time the "butterflies" returned in his older brother Sang-tae’s nightmares. Sang-tae, who was on the autism spectrum, had witnessed their mother’s murder years ago, and the trauma had tethered the two brothers to a cycle of running and hiding. Kang-tae was the anchor—sturdy, patient, and utterly hollow inside. He had learned to suppress every desire, smile through every insult, and exist only as a shield for his brother. Then came Ko Moon-young.