So either the Mangaka wants to play a fast one on us (still a possibility) or we are wrong about how "dark" this manga is. I mean even in his other Manga no one came closer to "trying" and killing someone in such bad attempts they were mostly not in danger(I think the most dangerous was shoving someone down a cliff) and the bad stuff mostly stayed in flashbacks I already can see this happening here. Are the Characters mentally ill? Yes, but not in the worst way yet.