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.
Moral Event Horizon: Lao Ye kills Shito's mother's fiancee on the night before the wedding. And when she committed suicide, he brought her back to life, just so she could be with him. He would later possess Shito's body and rip out Koyomi's "Dead Man's Tongue" in order to achieve it.
Squick: The fact that Shito's mother, who is a corpse, gave birth to Shito, who is also a corpse is just very disturbing.
Unfortunate Implications: The Big Bad is the only explicitly gay character in the series, and also a Camp Gay stereotype who regularly hits on and attempts to feel up teenage boys. Yomi also regularly attempts to grope and molest Mikuru, which Peach Pit apparently attempts to fix by explaining away that she's essentially a boy in a girl's body, which doesn't really make it any better.