The Witch: Part 1. The Subversion — Ending Explained

The central 'subversion' of the film is the revelation that Koo Ja-yoon never suffered from amnesia. Her entire persona as a sweet, naive, and memory-less country girl was a meticulously crafted facade. For ten years, she has been consciously suppressing her abilities and memories while waiting for the right moment to find her creators. Her motivation was not to recover her past, but to find a cure for the fatal side effects of her genetic modifications—excruciating headaches that would eventually kill her.

Knowing she couldn't find Dr. Baek on her own, she devises a plan: go on a national talent show and deliberately reveal a sliver of her power (levitating a microphone) to act as bait. She knew this would draw her creators out of hiding. Every event that follows—her 'frightened' encounters with Nobleman, her 'shocked' display of violence when her family is threatened—is an act. She allows herself to be captured and taken back to the lab precisely because she needs Dr. Baek to administer the temporary cure (the blue serum), which also happens to unlock her full power. Once injected, she drops the act completely. With a chilling smile, she reveals the truth and proceeds to dismantle the entire facility and everyone in it, including Mr. Choi and Nobleman. She wasn't the lamb being led to the slaughter; she was the wolf who built the slaughterhouse and sent out the invitations.

The film ends with Ja-yoon visiting her adoptive parents, giving them a supply of the serum to treat her mother's dementia, a gesture that suggests some genuine affection may have developed despite her manipulation. Three months later, she tracks down Dr. Baek's twin sister, demanding a permanent solution, revealing the hunt is far from over. A mysterious girl with a facial scar appears, whom Ja-yoon warns away, setting up the conflict for the sequel.

While the film's main twist is quite explicit, the ending leaves room for several interpretations and fan theories, primarily concerning the final scene.

• Dr. Baek's Twin as Ja-yoon's Mother: A prominent theory suggests that Dr. Baek's twin sister, whom Ja-yoon confronts at the end, is actually her biological mother. The cure for Ja-yoon's condition is a bone marrow transplant from a blood relative, which would give the sister immense leverage. This interpretation adds a layer of personal drama to the search for a cure, suggesting Ja-yoon may have to confront or coerce her own mother in the sequel.
• The Scarred Girl's Allegiance: In the final moments, a mysterious young woman with scars on her face appears. One interpretation is that she is another escaped experiment, potentially hostile and a new antagonist for the sequel. Another reading suggests she might be an ally or subordinate to Dr. Baek's sister, acting as her bodyguard. Ja-yoon's immediate threat to her implies a history between them, possibly from the original lab massacre.
• The Adoptive Father's Knowledge: When Ja-yoon leaves her family, her adoptive father alludes to having always known, or at least suspected, what she was capable of. This can be interpreted in a few ways. He might have simply put the pieces together over the years due to small, unexplainable events. A more complex interpretation is that he had a deeper understanding of her origins than he let on, perhaps even having some past connection to the organization, which would re-contextualize his decision to take her in.