Magico/YMMV

Badass Family: Shion is the father, Emma is the mother(not exactly Badass, but being able to be three hours in the Holy Spring Luna implies that she is stronger than normal people), Luu is the daughter, Anise the older and smarter daughter and according to Shion, the dragon is the son.
Complete Monster: Shion's older brother just showed up and he already gives off this vibe. So far he's bodyjacked a contest in the best couple contest so he could look at women, killed his mother, sacrificed countless people in an attempt to iron out the bugs in a ritual to make himself supernaturally powerful, and then tries to Mind Rape Shion into being his next test subject. And the magic he hopes to attain from sacrificing his brother is power over destiny to make himself a new life. It is even called the 99th Forbidden Magic. Possibly subverted when chapter 47 reveals that Faust is just lashing out at the world and Shion in particular because his own mother turned him into a literal monster.
- Shion's mother from the backstory. Sacrificed ten children to turn her younger son into a powerful demonic being and cast him out when the ritual handicapped him. Then she did it again using her older son and succeeded, turning him into a horrible demon. It's probably for the best that Faust killed her.
Harsher in Hindsight: Shion not being able to get the multiplication table right is funny until you find out that back in his childhood his physical and mental capabilities worsened after a botched Ritual.
High Octane Nightmare Fuel: Faust hanging out inside other people's bodies is creepy enough, but the way in which he comes out is always extremely disturbing...
- And then in chapter 41, when he takes his Psychopathic Manchild-ness Up to Eleven.
- Not to mention his true form, a strange demonic thing, revealed at the end of chapter 46.
Iron Woobie: Shion, especially after you find out about his backstory.