Angst? What Angst?: A complaint that was raised when Mai, Natsuki and Nao seemingly choose to allow the greatest tragedies in their lives to go forward in order to avert a temporal paradox in a trip to the past. The following chapters, however, indicate that the experience has forced them to realize how much those events have defined them and reconsider their priorities.
Complete Monster: Kirihara Hitomi is the first SUE to encounter the protagonists, and by far the most evil one. Initially bored with spending her time mind-controlling people to rob them, after being forced to kill a police officer and a witness, she discovered her darker hobbies. In the appropriately-titled chapter "Moral Event Horizon", Hitomi proceeds to commit her two most vile crimes. First, she brainwashed a police officer to slaughter twenty innocent people—including a baby, because her cries annoyed her—and commit suicide when he's done; then, she mind-controlled another officer into raping and killing his wife, only freeing him of her control to let him discover the act, before killing him as well. The first event was notably horrible enough to convince Nao to join the HiMEs to stop her. After capturing Mai with a mind-controlled Natsuki, Hitomi tried to torture her with her child's powers. She's only stopped from doing so by Shizuru's intervention, and dies from her child's destruction—which would normally result in the death of the person she valued most—showing how self-centered she is. In the end, Kirihara Hitomi is a sadistic sociopath who committed all of her crimes solely for her own amusement.
Moral Event Horizon: Discussed in the third chapter, titled this, which states that actions that should qualify as this for Mary Sues often do not in the eyes of their authors, and are not portrayed as such. Hitomi proceeds to cross it by using mind control to force a police officer to murder 20 innocent people, then commit suicidewhen he's done.
Shizune crosses it in her first appearance, by murdering Toki.