The Orphanage of Fear that Miyo Takano is sent to following the deaths of her parents is led by the seemingly kind Staff Leader who reveals himself as a sadistic disciplinarian by pretending to console Takano, only to immediately slap her in the face. Reveling in the brutalization of children, the Staff Leader rules the Orphanage with an iron fist, dishing out punishments to those he deems "disobedient." His crimes range from being extremely petty — such as forcing a boy to eat ink after he accidentally spilled some — to downright cruel. When Takano and three other kids attempted to escape the Orphanage, he sentences them to grotesque punishments with Eriko — the ringleader of the operation as well as Takano's only friend — receiving the worst one. She is sent to the chicken coop wherein she is pecked to death by the ravenous chickens. Takano herself is then made to clean an outhouse with her tongue. Despite being relatively minor in the series, the Staff Leader left a lasting impact on Takano's life, ultimately warping her mind, and making her the psychopathic, Godhood-obsessed mastermind she is now.
Teppei Houjo, while not on the same scale as other antagonists, more than makes up for it by being as despicable as possible. Teppei is made to care for his niece and nephew—Satoko and Satoshi respectively—after the deaths of their parents. A Child Hater to repulsive levels, Teppei subjects Satoko to a chilling series of abuse designed to humiliate and demean her. From forcing her to strip naked and using her as a table, to psychologically tormenting her, it's all but stated that he would indulge in sexually abusing her if she were older. Teppei commits embezzlement and fraud through badger games; uses his lover as a means of swindling men out of their money; and he takes sadistic delight from the ruination of their lives. Not above threatening people, Teppei murders Rika in one of the alternate worlds when she attempted to intrude. Selfish, cruel, and deplorable beyond belief, Teppei even manages to earn Miyo Takano's seething hatred. And unlike most other characters, Teppei doesn't have a mental illness for an excuse.
And of course there's Nomura. She could be viewed as the ultimate monster of the franchise as well. Being the Manipulative Bitch she was, she tricked Takano into helping her bio-weapon research and also indirectly influenced events that led to the Great Hinamizawa Disaster that claimed about 2,000 lives, all for no reason at all other than just to close up a company. And what's worse? She's a Karma Houdini.
Bernkastel. the Witch Of Miracles, reveals herself as a cruel sadist over the course of the story. Embracing her role as Big Bad in the fourth arc, Bernkastel set up Ange Ushiriyoma to have a hell of a life in order to manipulate her as a pawn later on before deciding Ange is of no further use and leaving her to turn into shredded meat. In the "game" on Rokkenjima island, Bernkastel introduces a pawn named Erika Fudo to mentally torment the mentally fragile Natsuhi by accusing her of being the murderer. She helps the elimination of the Golden Witch Beatrice to seize control of the game and cement the protagonist, Battler, in a forced role of villain. Bernkastel has no trouble admitting that her only real pleasure in life remains the suffering of others, and it's something she creates with endless amusement.
And of course, she ramps this up in Arc 5. She invokes Decoy Protagonist and Hijacked by Ganon when Battler refuses to play along and pulls out an actual Expy of Rika named Erika Furudo to serve as the new Protagonist. And Erika herself is a Bitch in Sheep's Clothing who immediately points the finger at Natsuhi, who currently is not having a good day. Which gets WORSE, now that being implicated for the murders brings her sister-in-law Eva's wrath down on her as the victims include her husband and Morality Chain, Hideyoshi. She also leads Battler to the Gold Room, which makes him the next successor, adding fuel to the fire regarding his family's stake in the murders. And manages to successfully disprove Beatrice, with Battler unable to help since he's too busy being IMPALED. Then Lambda makes Battler the Golden Sorcerer, effectively cementing him in the role of the 'villian'. Naturally, Bernkastel revels in this, until the point where Erika gets her ass kicked. She even has a smug 'Oh, did I piss you off?' look on her face at times.
Black Battler from Ougon Musou Kyoku CROSS is a negative palette swap of regular Battler who lacks the good-guy depths that his real counterpart does, not only talking about killing everyone on Rokkenjima but also suggesting to female characters that he's going to rape them, and he "tastes" male characters. He has a wicked habit of killing anyone he feels like killing, strictly For the Evulz, and laughing about it.
Yoshihito Kanamori from "Mesomeso-san" (the first chapter) started as the homeroom teacher of Marie Moriya, a young girl bullied by her classmates. He used to defend her from the bullies, until the stress of his job got to him and he started to take his stress out on Marie. His supplementary lessons include molesting her and putting it on camera. When Marie gathered up enough courage to stand up to him, he strangles her to death, singing her a song about graduation from life to death while doing so, then dumps her corpse in the old school's septic tank. He also considered murdering other children when he thought that they were eavesdropping. When he encounters Marie's spirit in the restroom, he gives her a long The Reason You Suck Speech about her not going to the police to report on him while she was still alive and called her an imbecile who couldn't fend for herself. He then opens the door to one of the bathroom stalls, and upon finding that Marie has apparently physically manifested, he tries to strangle Marie a second time. When the deed was seemingly done, he proceeds to rape the corpse when he notices it was still there. While he claims that he did all this out of love for Marie, it's ultimately proven hollow.
Nafumi Shintani from Renoir of the Art Room was an art room teacher who seemed to be a Cool Teacher, given her popularity among the young male students. In reality, Nafumi was a prolific child molester who got off on the suffering of young boys, deeming it as beautiful. To this end, she invites young boys into the art room, and she would offer them cups of drug-laced tea, after which she would proceed to torture their unconscious bodies with cigarettes and palette knives. In addition to this, she had dozens of sketches of abused boys in her desk. One of her past victims, Yuuki Noda, loved his teacher to the point that he allowed her to abuse him if it meant his feelings for her were returned. Eventually, Yuuki tried to escape her, but she grabbed his shoulder, which caused him to trip and fall underneath a table, resulting in a heavy bust falling on his head. A week later, she drugged and attempted to torture another boy, but she was stopped by the titular Renoir of the Art Room (who was really Higanbana filling in for the real Renoir). She expressed zero remorse for being indirectly responsible for Yuuki's death, stating that he was a "stupid kid" who deserved to die. Depraved and perverted, Shintani repeatedly showed that she cared only for herself and her lusts.