Soooo basically, after watching the new HTTYD film, I came up with the following headcannon:
21 years ago, the Night Furies were fleeing to The Hidden World in fear that Grimmel would hunt down every last one of them.
Unfortunately, Grimmel's armada got to them before they even had a chance to leave the archipelago, but, a few hours before, the two alphas of the Night Furies had entrusted their last egg to the Skrills, their distant cousins, just before their moment of death.
The Skrills had cared for their adopted hatchling, teaching it how to use the power of lightning as a weapon, though the Night Fury hatchling never used this ability until the events of HTTYD 3.
Once the Night Fury turned 15, he left the nest in an attempt to find the rest of his kind, oblivious to the fact that he was the last one. He searched the entirety of the archipelago only to get lost.
One night, he saw many dragons flying towards a volcano. Curious, he followed them, leading him to the main dragon nest, which became his temporary home. The Night Fury was a hated dragon to the Red Death for he would not steal food from the nearest viking village: Berk. Therefore, he was given the job of disarming the weapons system on Berk as the dragons raided.
A few weeks into the job, after blasting a catapult to bits, he was shot down by a viking boy, who would soon become his rider.
That boy's name was Hiccup.
