Sorry I haven't been active on the wiki for a while, but I'm aiming to create articles for the antagonists from the horror-comedy anime Ghost Stories after I've finished it. One villain in the series so far has really stood out to me as far, far darker than any of the others is Da Vinci, a ghost who murders innocent girls by transforming them into paintings. (The info I'm going to give here is from the English dub, which made changes to the story and characterisations).
Who is he/What's he done?
Da Vinci (real name unknown) was, in life, an art teacher at the old schoolhouse in the school where the anime is set. He developed a massive obsession with Leonardo Da Vinci, but despite his best attempts to match his idol's skill, his work was not well received by critics, leading to his suicide. He was later resurrected as a ghost, took the name of his idol, and developed the power to transform people, objects, and other supernatural beings into paintings.
The first thing we see Da Vinci do in the anime is murder an innocent girl, whom he had tied up and placed in a noose, and forced to pose for his artwork. He makes perverted comments about her breasts before absorbing her soul into his artwork, killing her. It's strongly implied that he has killed many other girls, since Amanojaku tells the protagonists that Da Vinci has a thing for killing young Christian girls, alerting them to the fact that their friend Momoko will likely be his next target due to her outspoken faith.
Around 30 years before the start of the series, the protagonist Satsuki's mother sealed Da Vinci away in a painting, but he was unintentionally brought to the present day when Satsuki unwittingly painted almost exactly the same painting in art class, creating a supernatural doorway for him to the present, where he targets Momoko. After using Satsuki's painting to travel back in time, he takes Momoko with him and is followed by Satsuki and her friend Hajime, who work with Satsuki's mother to try to cast a spell on Da Vinci to put him back to spiritual sleep. During their fight, he beats Satsuki's mother, has an impromptu rant about how much he hates ironing, then grabs Momoko by the shoulders, and kicks the stool she was standing on with a noose around her neck, attempting to kill her in cold blood. After which he attempts to leap back to the present, but is blocked by the painting being burned in the present day. When the painting was saved from burning by two of Satsuki and co's friends, Satsuki and her mother complete the spell, this time trapping him in a painting of his own.
None. He murders innocent schoolgirls for the sake of "art".
There are plenty of threats on a similar level to Da Vinci in the series, but (at least up to episode 15), he is one of only two who actually murder children. He's also probably the only one who isn't motivated by any grudge of any kind towards the world, and unlike the other example of a successful child murderer in the series (Babasare, who was born out of fear), he has no moral agency issues. Other ghosts who from the stories around them have also killed children also appear (e.g. the toilet ghost and the piano player ghost, but we know basically nothing about them or their motives, and they never actually kill on-screen, something that makes Da Vinci unique in the show (up to the point I'm at)). His killings are also probably far more heinous than what any of the show's other villains attempt, because when people are trapped in his paintings, they are trapped eternally. They experience no afterlife (unlike all other deaths in the show), and he is effectively damning these innocent children to eternal oblivion.
Obviously, this is up to you guys, but for me he's a serious game-changer in the show, and I really think he should be at least considered.