There is nothing subtle about the 500 times the MC declares he wants to be a hero, every character declares the supremacy of a third generation fire-starter, and flashbacks appear in every episode where he's called a devil. It's not only unnatural but repetitive.
Beyond that the animation is full of still shots and recycled establishing shots. The same images are used throughout different episodes and most of the show is actually still dialogue. It's as if they blew all their budget on 1min worth of combat per episode while the rest is just still frames with one character's mouth moving.
The final point I have is pacing. The pacing and editing detracts from any form of tension the show could've had. Flashbacks appear mid-combat, characters stand still for 20 seconds mid-combat, and characters hold 2 minutes speeches while the infernal waits for them to finish, again, mid-combat. For example, in episode two, the alarm sounds and Maki runs in to urgently alert the team. But when they get there, the captain spends 1 minute relating exposition outside the house accompanied with a still frame. Then he walks the recruits behind the house and takes another 4 minutes to explain. It's impossible for the audience to care about the world, characters, and combat like this. The pacing is completely uneven and there's no tension.
