This is generally an upbeat series, but there a few moments straight out of a horror film.
- Issei's death in the novel was bad, but in the anime, viewers get to see him desperately turn to run, get stabbed from behind, and fall to the ground and slowly bleed to death before Rias saves him.
- One of the worst was Juggernaut Drive. Issei goes into an insane berserker state, during which he CHEWS OFF ONE OF HIS OPPONENTS' ARMS!!!. He also grows a multitude of limbs from all over his body. And the real kicker? Ddraig has to warn Rias and the others to run away, because Issei would have killed them as well if they hadn't. The only reason this isn't High Octane is the way he was brought out of it. And this was only from Kiba and the rest's point of view. From Issei's point of view himself? It's a lot worse.
- The second time he almost pulled off Juggernaut Drive was when he got himself knocked unconscious by Sairaorg in their match. He then wakes up to a white world with the past Boosted Gear users, surrounded by dark aura. One by one, they tell him to pull off Juggernaut Drive to the point he joins with them.
- Diodora apparently made a habit of finding devout nuns and getting them branded as heretics. At which point he would rape and enslave them, as no one else would have anything to do with them. This is what would have happened to Asia if Issei hadn't saved her first. And all the more satisfying with the resulting Curb-Stomp Battle.
- Gasper's face when he snapped when told that Issei's dead.
- Kiba's past. All of his friends dying by being subjected to harsh experiments just so they can hold a holy sword while praying to God not knowing that God Is Dead in this series.
- Evil dragons in general. Considered by everyone as the most troublesome existences ever because they just love to destroy For the Evulz.