Google says this was a known torture method during the Joseon era. But in his case, they might’ve accidentally created a Taejagwi, which is a vengeful child spirit. A Taejagwi is usually created through a whole ritual process (basically black magic but make it shamanism). Still the soul binding part of it kinda makes sense here. He still remembers his past life and in a way, hasn’t he taken over Yooyoung’s life?
I also think the present version of him having black and white hair might be a clue. Yooyoung had black hair while Yooyeon had white hair in the past, so the mixed hair could symbolize that he’s not fully himself anymore but not fully Yooyoung either.
Google says this was a known torture method during the Joseon era. But in his case, they might’ve accidentally created a Taejagwi, which is a vengeful child spirit. A Taejagwi is usually created through a whole ritual process (basically black magic but make it shamanism). Still the soul binding part of it kinda makes sense here. He still remembers his past life and in a way, hasn’t he taken over Yooyoung’s life?
I also think the present version of him having black and white hair might be a clue. Yooyoung had black hair while Yooyeon had white hair in the past, so the mixed hair could symbolize that he’s not fully himself anymore but not fully Yooyoung either.