- "You never cease to amaze me, bud. Thank you."
Hiccup and Toothless have a very close bond that has gotten stronger as the franchise has gone on. Hiccup and Toothless lead Berk as alphas of their respective species'. They first met in the first film of the franchise, and have been featured in every show and film to come.
He later goes in search of the dragon he shot down, experiencing a lack of success he vocalized quite frustratedly, right before he finally stumbles upon his first clue of where the dragon fell. Approaching the crash site carefully, albeit in some haste, he follows the trail the Night Fury made on the ground during the crash landing before suddenly spotting the dragon's sprawled, restrained form over a mound and ducking in shock. In a series of tense moments, he slowly works up the courage to first expose himself slightly to look at the scaled beast, before slowly approaching it after drawing his knife and defensively moving toward the incapacitated reptile. After peering around a rock he'd hidden behind that obscured proper vision of the Night Fury, he realizes that the bola had completely immobilized the dragon (who initially appears dead or unconscious), and his ecstasy finds him once again as he believes his tribe will finally think highly of him, and take him seriously. In his celebratory moment, he places his foot proudly on the Night Fury's shoulder while proclaiming that he had "brought down this mighty beast", before the dragon, still very much alive and conscious, shrugs him off with a loud, somewhat pained grunt, putting the boy on the defensive again as he realizes that the dragon may yet pose a threat. As he brings his knife to bear once more, he cautiously approaches once again, and this time finds the dragon peering at him out of the one eye facing him.
The timid teen nervously looks back at the dragon, before slowly working up and building up the courage and bloodlust necessary to use the knife on his catch, telling the waiting reptile (and mostly himself) that he would cut out his heart and take it to his father, and that he was a Viking, feeling the need to repeat the last point in a more aggressive tone before he raises the knife over his head. He looks back at the dragon one last time, the beast never having taken his eye off him, before the former closes his eyes and grits his teeth once more. The Night Fury also closes his eyes, letting his head drop in despair as he awaits the killing blow... which never comes.
Unable to bring himself to slay the beast, Hiccup looks at the dragon, still awaiting his fateful end, before expressing disappointment in himself at having even shot him down in the first place, realizing that he didn't have it in himself to kill him. As he walks away dejectedly, he pauses and looks back at the downed beast, realizing how helpless he was in his shackles, still awaiting his end. The Night Fury's eyes suddenly open as he hears a cutting sound to his side, and looks to his left as he realizes that Hiccup is cutting away his restraints. His bound limbs come free, and in an instant he pounces on the boy, pinning him to the rock behind by his neck and chest, sending the latter into a panicked state as he looks up at the dragon, who gazes back sharply through narrowed pupils as he regards his former captor. As the intimidated teen squirms in terror, the dragon looks on for a second more, rears up and takes his foot off the boy's torso as he emits a loud, fearsome roar (right in his face), turns heel and leaps out of the clearing and into the undergrowth, attempting to take flight as he does, but crashing into a rock and a few other things as he fails to do so, disappearing from sight altogether. A very shocked and spooked Hiccup turns to make his way back (but not before comically collapsing once out of sheer relief and recovery from his terror).
The next morning, following the teens' first dragon-slaying class, the course of which very nearly saw Hiccup blasted to death by the arena's Gronckle before being saved by Gobber, the students (and Hiccup in particular) are warned by the blacksmith that a dragon will always, always go for the kill. Later, Hiccup revisits the site of the Night Fury crash, picking up one of the bolas on the ground as he wonders out aloud why the dragon he freed didn't do the same. His curiousity getting the better of him, he makes his way into the forest, in the direction the dragon disappeared in, eventually finding himself in a niche opening out into a large, secluded, naturally formed pit-like clearing with high rock walls and a lake in the middle of it. He looks in and sees no sign of the dragon inside, remarking in disappointment that it was stupid to even try and find him again, before some black dragon scales on the floor of the niche draw his attention, and he crouches down to look at them. As he picks one up and examines it, the dragon suddenly bursts upward from the floor of the pit (previously concealed by the peripheral blindspot of the niche) toward the top of the wall, right in front of the opening the boy is in, causing him to fall backward in shock and fear. The Night Fury attempts to scramble onto the top of the wall, but slides back down as he haplessly claws at the rock, unable to find purchase, before attempting to avert a hard, awkward landing by leaping off the rock and pivoting to glide back toward the ground, crashing nonetheless as he nears it. The inquisitive teen moves out of the niche and jumps onto a sloping rock platform just below it (nearly sliding off and into the pit in the process), trying to get a closer look.
Hiccup takes the opportunity to make a quick (and surprisingly detailed) sketch of the dragon in his book as he observes him attempting to take flight and escape the clearing several times, each attempt culminating in failure. It is then that the boy wonders why the Night Fury doesn't simply fly away, realizing as the dragon fires off a shot into the ground nearby in exasperation, that one of the reptile's tail fins is missing, likely lost during his crash landing in the forest. He accordingly smudges out the corresponding tail fin in his sketch, surmising that both fins must be required in order for the creature to achieve steady flight. This theory appears confirmed as the dragon attempts flight once more, his tail stalling out and ruining his flight-form mid-air, dropping him onto the ground once again. As the Night Fury lays there exhausted and frustrated, a fish flops up and back into the lake nearby, and the dragon gets up to try and catch himself some food. He plunges his face into the water, hoping to snag one of the fish swimming around near the surface in his jaws, but fails to do so. Hiccup, watching from above at the other end of the pit, feels sorry for him, and accidentally drops his stylus into the clearing. It bounces off some of the rocks, catching the reptile's attention, and causes him to look up. He recognizes the boy, and they both warily look at one another out of curiosity.