Designated Hero: Yayoi. Her motives (the desire to get her mother back from the ghost that kidnapped her) are sympathetic, but the way she goes about it is not—she enslaves and tortures ghosts to make them fight for her, even encouraging them to fight among themselves to create stronger monsters at her disposal, and generally commits Pay Evil unto Evil to the ghosts to a brutal degree, something that even takes Keitaro aback. What's worse, it's made clear in the series that the ghosts, even the Always Chaotic Evil vengeful ones, used to be people at some point instead of demons or creatures of pure hate. However, Keitaro is the only character to ever even express slight concern at her tactics, and even that's in a Lampshade Hanging way, as he still views her as a little sister he wants to protect despite being very familiar with how cruel she can get in pursuit of her ultimate goal.
Jerkass Woobie: Several ghosts qualify, but perhaps the biggest example is Black Asura of the Eclipse. He's an abuse victim who was horribly mistreated by his stepmom. She later murdered his father and turned his body into meatballs, causing him to unknowingly eat his father before later being murdered by his stepmother to hide her crimes. Tellingly, he's one of the very few ghosts who Yayoi has sympathy for.
The entire Annunciation House arc is practically squick incarnate. Eiko subjected to copious amounts of Womb Horror with Angel, the ghost who Yayoi and Eiko encounter there, being a giant deformed fetus. The real kicker though is Angel's backstory in which Saki rapes her father, has him impregnate her, and sacrifices the child to allow its body to become a host for Angel.
The A Dam ghost is essentially a serial rapist who kidnaps men and repeatedly violates them for her own pleasure.
What Do You Mean, It's for Kids?: Dark Gathering is published in a shonen magazine and features zany comedy, Mon battles between ghosts, and a Kid Hero with a rather cartoony character design. However, the series will repeatedly go out of its way to remind the reader that it is still a horror manga first and foremost, with all of the gore, brutal violence, Body Horror, hellish abominations, and (at times) sexual violence that one would expect from the genre.
Ai Kamiyo. Poor girl became the target of a sadistic god who intended to turn her into his plaything for all of eternity, causing her family to cast her out and for her to only have her brother to rely on. Eventually, her brother was killed in an accident, only for her brother's ghost to try to kill her for the sake of protecting her from the god's cruelty.
Mr. Sakashita. A kindhearted teacher who wanted nothing but to help his students, only for him to become the target of cruel harassment at the hands of his students. Eventually, one his students stole his phone and took photos of herself to falsely accuse him of being a pedophile, causing him to get fired and for his family to leave him in disgust. His situation was so dire that he committed suicide while setting up an occult ritual to enact vengeance on the students who ruined his life, yet even then he didn't become an evil spirit due to his genuine compassion for children stopping him from ever acting on any kind of killing intent. In fact, he would have ended up passing on peacefully if it wasn't for Dorothy manipulating his ghost to artificially amplify his maliciousness. At least the poor guy is finally able to pass on in peace after Yayoi defeats him...
Woolseyism: One fan translation replaced the first example of Yayoi's Catchphrase with her singing the Ghostbusters (1984) song. It was not what the original text said, which is why the official translation just had the catchphrase. Unfortunately, it was also very funny and set the tone of the series perfectly.
