I really enjoyed Atsutashi's emotional scenes. When Lo cried for the first time, I was surprised; when Iwao was struggling with intense emotional angst, I felt that; when Celi fought Urui, I felt terror (and also like Urui might have been going easy on her).
The magic system (Firia) was neat; I liked the explanation given about how you could 'charge' certain spells up to a point, then charging them any more would be a waste of firia. I also liked how much of a threat the king was; there were several moments throughout the battle where I thought that the heroes might lose just because of how imposing king Benegram was.
The way the creature's vow of revenge ended up coming true was very narratively satisfying; while I tend to prefer happier stories, the act of a vow or promise made long ago coming true reminds me of J.R.R. Tolkien's 'Silmarillion.' In the Silmarillion, Maeglin (a dark elf) is cursed by his father to die via falling from the city walls; and despite Maeglin's best efforts, he dies the same way his father did. In an era where so many prophecies are subverted or cast aside, I find Atsutashi's follow-through on the creature's promise delightfully refreshing.
The 'Annihilation Wars' were a fun concept, and the fact that the creature that tormented Iwao was involved in one of them was a twist that I did not see coming; the ramifications this has on the story are interesting, and I would have enjoyed seeing it be more relevant.
Another thing I particularly enjoyed were the nightmares.
Each nightmare conveyed the themes and ideas it had clearly; Lo's loneliness was evident within his nightmare; Celi's trauma was clear in hers; and Iwao's nightmares always managed to show what he was feeling well.
The concept of 'nightmare eating' is not wholly original; yet I find Atsutashi's take on the matter to be both visceral and enjoyable; he goes in detail to describe what it feels like for Iwao to consume each nightmare; how it fills him and leaves his victims feeling peaceful.
Yes, there were some grammatical errors.
Yes, there were some contrived moments.
No, they did not ruin the story or disfigure it beyond recognition.
Overall, I think Atsutashi's 'Fear the Night' is a worthwhile read, and something that can be enjoyed and speculated about for a long time.
I cannot wait to see how Atsutashi improves in his next novel.

(This review has been revised due to a realization of how sharp the last one was.)