It's implied that the villager head assaulted teenage Haesu - can be left to interpretation as it's never directly said what he does to her (whether or not it was just a violent attack).
Hyeon-su's biological father encourages him to harm a rabbit. The ensuing harm is not shown on-screen or mentioned. nor is it confirmed if it even happened at all.
Hyeon-su's mother is physically (rarely) and (frequently) emotionally abusive. His biological father is implied to have been abusive and manipulative. Hyeon-su and Ji-won's daughter is never abused by them.
The accomplice's parents are shown to be very strict, occasionally even emotionally unstable and physically abusive to him. It's implied that he was also partially groomed into his violent behavior by another adult.
If you're especially sensitive to the portrayal of mentally ill people as criminals, I would stay away from this show. The protagonist, Hae-su, is diagnosed with Antisocial Personality Disorder, and was violent as a child and ismanipulative as an adult. However, he is portrayed as a sympathetic character who is capable of human emotion just like anyone else, and just displays it differently, struggling because of a lack of care and understanding from others.
should preface this by saying pretty big SPOILER WARNING for a couple of twists in the show, and also by saying that the main character's child (the most prominent child in the show) is NOT abused. the main character's parent is not shown as directly abusive, but is a serial killer who it is implied is trying to influence his son in the same direction. the main character's 'parents' are also cold towards him and his child, and he was also forcibly exorcised multiple times by a guardian figure as a teenager. the plot of the first few episodes involves a child possibly being pushed down the stairs by his father, and although this is not the case, the theoretical incident is shown.
Skip forward a bit when you see the victim's mother pull out a bottle of multivitamins; there is a live cockroach inside and when she sees it she instinctively drops the bottle and we see the bug skitter away on the floor.
Episode 1 has two scenes: 1, a flashforward where the two protagonists are underwater, one restrained and the other trying to free him, and 2, when one character attacks another character and suffocates them into unconsciousness.
In the show, Hyeon-su is abused because he has Antisocial Personality Disorder. However, some of his behaviors, such as struggling to understand empathy, disliking certain sensory stimuli, having difficulty connecting with others, and being seen as "weird" and "creepy" may resonate with people with autism.