Much like how well meaning grandparents will let their children read Watership Down because its just a silly book about rabbits, how bad could a rabbit book get, the How To Train Your Dragon series has a veneer of childishness and humor that overshadows its darker subjects. Further, the HTTYD movies are family films through and through, no matter how sad or violent they may get.
And, since that childish, humorous veneer is so thick at the beginning of the series, and because the movies differ so much from the source material, the HTTYD books get treated as just another silly children's series as a result, and the fact that they are prime examples of modern gothic literature is generally left unexplored.
If I had majored in Literature I could give you a comprehensive run down of what gothic literature is, and if I had ever finished this series and/or read the books that I do have within the last 5-10 years then I'd be able to connect it beautifully to the text with citations and everything, but dammit Jim, I'm a mathematician with health problems, so bullshit and half remembered genre conventions are going to have to do.
One of the main, lasting emotions in HTTYD is fear.
Oh sure, it might not seem like it at first. Hiccup is almost constantly afraid until he gets hit with the ADHD hyperfixation zoomies (relatable), Fishlegs is almost always afraid until he gets Enraged™ (also relatable), Camicazi is Very Definitely Not Afraid until things inevitably Get Worse, Toothless....well, Toothless isn't afraid until he's the one being threatened or he momentarily gets over his selfish nature. But, most of this is played off as humor, and we the readers aren't really afraid, regardless of what the characters feel.
Until, you know, the end of the first book.
Or those couple of chapters in the second book (the one about the baby dragon especially).
Or a fair bit of the fourth and fifth books.
Or almost the entirety of the eighth book and onward, especially that one fucking witch illustration (and isn't that interesting too, that the messy scribbles found throughout the series go from looking like childish doodles in the early books to something horrifyingly desperate, like the scratchings of a madman staring into death's eyes?) that has haunted me for years.
And yeah, sure, it's a very cartoonish sort of fear, the kind of fear where you're well aware that this is fiction and Not Real, so it doesn't actually matter, not really, not like it would if something bad was actually happening to you.
But it doesn't change the fact that these books are positively dripping with fear. Bathed in it. To the HTTYD books, fear isn't the one time a serial killer takes an interest in you, or the one time someone brings home a cursed doll. Fear is something inevitable. You can run from it, you can soften it with silly names and fun chapter titles, but you cannot escape it. Fear is the inevitable trajectory of these books. Like death. Like fate.
Which, as it just so happens, comes up a lot in HTTYD as well.
Much like the role of fear, the role of fate in the HTTYD series ramps up with each book. It's faint within the first book in comparison, but still present--Hiccup brings up fate quite a bit with regards to Toothless and his place in the tribe, for example.
The fourth book deals a lot with the idea of escaping fate, if I remember correctly, as does the seventh book, though that's more of changing fate, or more accurately, an ax.
The sixth book (again, if I remember correctly) starts to play with the idea of Hiccup's fate as the third Hiccup Horrendous Haddock in particular, which, as far as I know (yet again, I never finished this series) is basically The Entire Point of books eight and onward.
Alvin the Terrible is fate and fated.
Hiccup's mere existence runs withershins to the pull of fate, given who his mother had been fated to marry.
There are prophecies, and omens, and ghosts, and the songs of the dead (quite literally!) throughout.
Fate and fear are the bones of this series. Its atmosphere and aesthetics only add. The connection between Bad Things Happening and the environment is clear throughout the series, and its use is undeniably gothic in nature.
Gloomy weather is for brooding, sunshine is for brilliant escape plans. Fortresses loom. Home is bleak and muddy, and other islands are either untamed wilds home to horrors inside, or even more bleak because Something ate up all the life.
The sea is an unsurmountable distance between the Parent and Child that cannot understand one another, a depth that hides friend and foe alike, the thing that separates one consciousness from another, tribe from tribe, that which is to be feared because it is known and that which is to be feared because it is unknown.
The bird sings whip-poor-will.
The HTTYD books are gothic literature, but most folks never got far enough in the series to see them as such because they were introduced to them from the movies and expected something quite different, and those that did read them are not dissimilar to the saying about boiling a frog since the shift to darker and darker material was so artfully gradual. There's a lot more to be said about just how gothic HTTYD is (the villains, the plots, the conflicts, the way each book builds from the previous, the use of book six as both a resting point and as exposition, the role of dragons as the gothic, etc. etc.) and the genius of Cressida Cowell, but I've made my point and now I'm going to lie in it.
Consider the threat fulfilled.
