Incidentally, as someone who wants to go into forensic psychology, people who commit violent crimes almost always come from an extremely troubled background where really their family was at fault, often for outright abusing them like in Shion’s case. I think the responsibility lies more on the family’s shoulders - Oryou obviously treats Shion awfully, and by extension you could say Akane is at fault for not interfering with that or at least adequately expressing to Shion that however the family acted on the surface, she shouldn’t take it to heart. They are adults, Mion and Shion were children. It’s the role of adults in a family to look after those in their care. I don’t think there was much Shion could have done, she was placed under too much pressure, and she snapped. That pressure was instigated from childhood by the adults in the family, and nothing was given to compensate for it. The problem is that Shion never in the first place felt her pain mattered to anyone around her, knew anything besides pain, or felt like she deserved anything else. That is the fault of the environment she grew up in, and what’s so tragic is that no matter what she’d done, it was up to them to take that away.