The simple premise of the fan game: everyone except one person is a criminal in some way, shape or form. While some range from relatively harmless like Dracul's shoplifting or Kotaro's cheating, other revealed crimes are more insidious. The murderers in particular have some very twisted crimes.
Kiyoshi engages in Muse Abuse, kidnapping girls to be used as ways to catch the emotions of others.
Emilia set her father's hospital on fire while patients were still in there, causing immense harm to the innocent patients and killing some of them.
And while it may have been a joke, Mononeko mentions someone there is a bioterrorist.
Shinku is not in a good state, hallucinating nightmarish outlines of his sister covered in eyes, and as more deaths come, he hallucinates them as well:
Dracul is a purplish shadow covered in eyes and lines resembling devil horns and horns.
Ismene may have murdered her professor, but that professor is a nightmare in and of himself. A much older sexual predator who preyed on Ismene's anxiety about her grades, he engages in Blaming the Victim and talks in a soft, yet obsessive voice, making her perform favors in exchange for improving her grades.
Let's stop playing games, my dear - what else were expecting when you wear that adorable little uniform? God Ismene, you're killing me here! You're just so...irresistible! I can't keep my hands off you...!
The first murder. In contrast to the relative simple stabbing and smashing of the canon games, the first murder is among the most deranged: Dracul was disemboweled and put aloft a giant cake, his eyes taken out and topping it while his intestines wrap around the cake like streamers. Lyra saying that the killer wasn't the most sane is an Understatement.
On that note, the killer: Maiko Yuzuki. As a result of a horrible Stage Mom, greedy stepfathers and a complete lack of support, she's been warped into a Serial Killer operating under a horrifying combination of Black-and-White Insanity and All Crimes Are Equal. Dracul's shoplifting was apparently as bad in her eyes as Ismene's murder, Taka's tampering with evidence, Kotaro's fraud, and Kiyoshi's kidnapping, and anyone helping criminals or arguing for their defense is just as bad in her eyes, deserving of death.
When Rei breaks her worldview and calls her a delusional coward, Maiko's Villainous Breakdown is not a pleasant one. She claims that everyone else is delusional, and not her, and that her mother must be possessed by evil with how she keeps bringing in greedy leeches as stepfathers. It just paints how badly her career as a child actor and lack of a support system destroyed her mind.
Maiko's execution: Un-Magical Girl. The execution starts out fairly tame, having her admit to murdering a man and that she was never a good person. Each time she says a phrase, arrows fire into her legs. For the third line, she has to admit that she's not Melody Pretty. However, because being Melody Pretty is such a core part of her identity, she can't do it, and this causes the room to be set on fire, leaving her to futilely slam on the window as the flames engulf her, leaving only her crown.
Taka's situation in the investigation portion of Chapter 2. Imagine witnessing a murder and then almost becoming a victim to silence you, even when you can't talk.
Yui Aoide. Holy fuck, YuiAoide. This game's equivalent to Kanade Otonokoji does not hold back in being as nightmarish as her. But let's talk in depth about why she deserves her own section.
Like Kanade, she's also got her own gallery of Nightmare Faces, showing just how cuckoo she is, and her voice also tends to suddenly deepen when she gets particularly angry.
On the note of narcissism, she checks all nine attributes of one according to the DSM. It normally only takes 5 to label one as such, and she's among the most frightening descriptions of how dangerous a narcissist can be.
Grandoise sense of self-importance (She continuously believes that she and she alone deserves to escape, willing to condemn everyone else to death)
Obsession with idealized fantasies of power and status (Her obsession with having Eiichi as "her prince" and of gaining fame for her story of survival)
Belief that she must be around other special people (She decries the other Ultimates as maladjusted adults and disgusting filth, thereby beneath her status)
A need for admiration (She constantly keeps calling herself special and is smarter than all of them combined when confronted about her murder)
Lack of Empathy (She's dismissive of the horrible things that happened to others, such as Ismene's professor being a predator and Lyra's desire to keep her criminal past a secret from those she cares for)
Jealousy (She repeatedly tries to keep Eiichi's attention on her)
Arrogance (She's extremely proud of what she does and how she looks)
Her relationship with Eiichi is horrible and a complete Aversion of Double Standard: Abuse, Female on Male. Her acts against Eiichi are depicted as horrific acts of abuse, causing him to become a shut-in. She completely ignores the fact that he's gay and believes she can change him, doing everything in her power to make him hers: cutting him out from other girls in his life, physical, verbal, and sexual harassment, stalking him on social media and real life, blackmail, threats, and even SWATTING him by claiming that he was committing her crimes. The last of these ended up leaving the poor boy's father unable to work as the result of a back injury. When she tries to get him to love her under the effects of Rei's hypnosis (something similar to propositioning someone under the influence of drugs and thereby not completely cognizant), his rejection leads her to decide to murder him, letting out all her frustrations.
Yui's execution, ''Chaque Rose a son épine" is as nightmarish as she is. Her legs are cuffed to a stage as a spiky vine wraps around her neck alongs a similar metallic ring before getting blinded by spotlights like she did to Eiichi. She is then forced to conduct an orchestra of Mononekos for an audience, who soon start to boo and throw stones at the stage. When the music starts worsening, the metallic cuff tightens, garroting and stabbing her neck before decapitating her.
Her habit of always smiling can come across as pretty unsettling, especially when she's otherwise crying or looking dead inside. Apparently, Alora provided her sister with medication so Takiko can't even feel negative emotions anymore. How effective that is remains unclear.
After her mother died in childbirth, her father was left to raise her and Sachiko on his own. This went on for about eight years until, out of nowhere one day, he waited until Sachiko was out of the house, then took Takiko on a drive to a bridge and drove right off the side. While Takiko survived, the event left her in and out of a coma for five years.
In one of her bonus scenes with Shinku in Chapter 3, after a pretty normal conversation, she points out that Shinku seems to like talking to ghosts. When he tells her ghosts aren't real, she asks about the shadow standing behind him. She doesn't elaborate any further.