Hiccup Haddock ¹

A long time ago, Vikings created a book of dragons where they wrote everything about each species of dragon, about their powers, strengths, weaknesses, etc., all dragons except for one that nobody knew anything about.
When Stoick and Valka had Hiccup, the first thing they did was talk to him and teach him about the book and the whole story about how to train your dragon. Hiccup found Toothless, the Night Fury who became the alpha.
And everything was going perfectly well. Hiccup had never even touched that book of dragons, because only those who explored beyond the Seven Watches of Berk read the book to find out which dragons they would encounter and rescue.
But then Hiccup enters the picture. He was curious, perhaps too much for his own good. One night, it was snowing, and he left his house—he lived alone, since he was already 22 years old—and went to the library. He secretly took the book and read everything, absolutely everything, until he reached the last page.
There was absolutely nothing on the sheet, no writing about power, strength, or size, just a single name (choose the species name), and right below it, in tiny letters that he could barely read in the dark, it was written...
'When the sun and moon were offended by humankind, they sent them a punishment: a huge dragon that is the very mixture of the sun and the moon. We never saw anything of it; it arrives, attacks, kills, and leaves without ever being seen. No one has ever managed to tame this dragon. Never approach it or the border of its island.'
He said nothing more, he didn't say where the island was, where the border was, he said nothing more. But if Berk tamed dragons, why not try? And he remembered that hunters disappeared soon after passing the seven borders of Berk and going north, very, very far from Berk. And one thing he knew: he was too stubborn to leave a dragon like that alone. He was going to try to tame the beast that no one had seen, and yet everyone feared.