These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
There's also the matter of whether his stalking Misaki is funny, or creepy? The manga has examples that can be argued either way. For instance, when he and Kadotake bond over a CD that has recordings of Misaki using the bathroom, is it funny? Or is it disturbing that a couple of guys would bond over an invasion of a woman's privacy?
Bile Fascination: Kadotake's interests in Misaki's career as a dominatrix can be interpreted this way. On one hand, he considers it a dodgy line of work and he's even snarked about it. Yet, he's always eager to hear about the details of the type of S&M play she does with her clients and has a morbid fixation about her piss and whether they drink it.
In chapter 5, Shizue arranges a photo shoot for a lesbian magazine, featuring herself and Misaki doing S&M play. During the shoot, Misaki could tell Shizue was getting off on it, which she confirms afterward, when she tells Misaki the shoot got her excited and that the photos should be enough to last herfor days.
You know she's da bomb when a magazine company asked her to offer a pair of her panties as the first place prize for one of their contests. While, in the manga, not only is she one of the most frequently requested Doms at the Roppongi S&M Club, but Gorou Oukawanote a famous and very popular former pro wrestler, who's one of their most valued patrons will only seeher!
Moral Event Horizon: Koga's attempt to rape Ai, in the first episode, was already heinous to begin with. But a flashback eventually reveals he broke into her sister's home and tried to rape her as well, but was interrupted by Miku, her sister's 2 year old daughter, who was playing with her teddy bear. So he took it from her, causing her to tug on his hand to try to get it back. Koga tried to yank his hand away, but Miku's grip tightened on his fingers, which sent her flying across the room and through the window to her death. Which caused Ai's sister to blame herself and take her own life.
The manga version plays this out differently. As in the anime, Miku's death was unintentional but, instead of dying at the scene, she dies at the hospital, due head trauma and internal hemorrhaging. However, Ai's sister wasn't home at the time that it happened. Instead, she flees the hospital and commits suicide out of grief for her daughter.
The Woobie: The emotional turmoil Ai goes through while trying cope with the deaths of her 2 year old niece and her older sister, is bad enough. Then Koga makes it worse by attempting to rape her, when he finds her alone at her sister's abandoned apartment. Her only solice is "Po", the stuffed bear she'd given her niece as a present.
Even after the truth surrounding their deaths is resolved, she adopts "Po Po" as a coping mechanism. And just when you think life couldn't screw her over, any more that it already had, she gets attacked by a vengeful spirit that had possessed a stranger she was trying to help. It's no wonder she brought out Misaki's'big sister'instinct.