Rio displays symptoms of a major depressive disorder (persistent low mood, inability to experience pleasure, rumination over real or imagined failures, memory loss), severe trauma (dissociation, insomnia, nightmares, inability to imagine a future), and borderline personality disorder (history of trauma and abandonment, and an intense fear of the latter; dissociation; emotional dysregulation; extremely weak sense of personal identity; a pattern of chaotic relationships, where she first pressures her partner into intimacy, then begins pushing them away; impulsive behavior, up to and including self-harm and suicide attempts). In addition, Dr. Minori suspects she may be neurodivergent, even if not to the same degree as Sahoko.
Sahoko is much more ambiguous, as the cause of her two-year hikkikomori phase is never established for sure. Dr. Minori speaks of "different sensibility", potentially alluding to some kind of neurodivergence.
Moral Event Horizon: Shigeko trying to provoke Rio into suicide. Even worse is, upon being called out on it, she not only showed zero remorse for it, but appeared to be genuinely offended that her husband and Shoumitsu were "taking Rio's side" on the matter.
For the film:
Cry for the Devil: Kang-do has committed a lot of cruel and despicable acts, but it gets extremely hard not to feel bad for him, as during his Villianious Breakdown when he becomes emotional over Mi-sun's "supposedly" missing and death is heartbreaking to watch.
Signature Scene: The ending where Kang-do chain himself to truck underneath, leaving a trail of blood on the road while the truck drags his body.
Too Bleak, Stopped Caring: There are almost no sympathetic characters in the movie- Kang-do is a cruel, violent jerk, Mi-sun is manipulative, and all of Kang-do's victims are somewhat pitiful but vindictive and weak-willed. Combined with the brutal violence, this makes the movie a tough watch.
