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: When you learn that Maou used a terrorist attack in Russia as a convenient way of killing Kaoru Mishima, Haru's mother, simply because she is the wife of the person who ruined his father's life, you will despise him, if you have not already done so when he kidnaps Tsubaki's kid brother, Hiroaki, then proceeds to corrupt the poor girl.
Suspiciously Similar Song: Practically all of the background music used is a variant of famous classical music pieces, ranging from Bach to Wagner to Grieg.
Villain Decay: Mephistopheles/Saijou in chapter three initially comes off as a cold but honorable right-wing extremist, later he is revealed to be more of a sociopath who is easily manipulated and controlled.