How do friendships define us?

“How to Train Your Dragon: The Hidden World,” Dean DeBlois’ third and final film in the series, searches for the answers to that question in a heartbreaking and nostalgic conclusion reminiscent of Pixar’s “Toy Story 3.”

The film begins with Hiccup, voiced by Jay Baruchel, leading his friends on a raid on a dragon trapper ship. Immediately, the audience sees the personalities and strengths of each supporting character, with Hiccup’s longtime girlfriend Astrid, voiced by America Ferrera, showcasing her strength and battle tactics and Hiccup using his ingenious inventions.

As Hiccup’s inventions grow loftier and more creative in each series installment, “The Hidden World” gives the village chief a suit of dragon scales that makes him fireproof.

Once Hiccup’s team successfully rescues the dragons and returns to Berk, the village over which Hiccup rules, the villain is introduced. Voiced by F. Murray Abraham, Grimmel the Grisly quickly sets himself apart from the series’ other villains. While the antagonists of the first two films are bulky, slow-moving characters whose considerable brawn is their greatest asset, Grimmel is lean, intelligent and more ruthless than his predecessors.

Prior to the series’ beginning, Grimmel murdered all other Nightfuries, leaving Toothless as the last surviving member of his species, and he’s determined to see dragons go extinct. Releasing a captured Lightfury as bait for Toothless to follow, Grimmel stalks Hiccup and his people, first setting Berk on fire then following the villagers as they travel across the ocean to escape Grimmel’s wrath.

In a desperate attempt to protect both his people and dragons, Hiccup leads the villagers in a search for the Hidden World, a fabled land where dragons live safely. Meanwhile, Toothless meets and falls in love with the Lightfury, prompting Hiccup to build a machine that allows Toothless to fly on his own, without a rider helping him steer with his broken tail.

The theme of friendship and growing up shines in these moments — although it clearly breaks his heart to set Toothless free, Hiccup understands he cannot keep his best friend away from the Lightfury forever. With Astrid’s constant support, Hiccup watches Toothless fly on his own and prepares for a long day without his friend by his side.

While Toothless and the Lightfury fly together, the Lightfury shows Toothless the Hidden World — a veritable paradise filled with dragons of every imaginable species, vibrantly colored plants and glowing crystalline structures. Although Toothless finds a place truly meant for him, Hiccup realizes he needs his friend more than ever, as he and his team decide to attack Grimmel in a preemptive strike that only results in the heroes and their dragons nearly getting killed.

Ruffnut, one of Hiccup’s friends, is accidentally left behind when Hiccup and his team escape, though she is quickly released and followed by Grimmel and his henchmen.

Desperate to protect his people and unable to accept that Toothless may be gone forever, Hiccup searches for the Hidden World with Astrid, but, upon finding it, realizes the dragons who live there are hostile toward humans. Toothless and the Lightfury help Hiccup and Astrid escape, though Toothless is visibly furious that he had to leave his newfound sanctuary to protect Hiccup, but before the friends can find a way to repair their relationship, Grimmel appears suddenly to capture Toothless and the Lightfury.

The villain uses Toothless’ powers as an alpha dragon to convince the rest of the dragons to follow them, leaving Hiccup and his people powerless.

Relying again on the support of Astrid, Hiccup devises a plan to use one of his inventions, similar to a modern-day hang glider, to chase down Grimmel’s ship and rescue the dragons. Upon releasing Toothless and once again flying with his friend, Hiccup leads Grimmel away from the fight and higher into the sky, where Toothless can fully utilize his strength as a Nightfury.

With Grimmel following Hiccup and Toothless on the Lightfury, whom he brainwashed using dragon venom, the chase ends abruptly when Grimmel knocks Toothless unconscious with a tranquilizer dart. Sacrificing his own safety to free the Lightfury from the mind-numbing venom, Hiccup knocks Grimmel from her back, and the two tear at each other as they plunge toward open water.

In a moment both breathless and poignant, Hiccup begs the Lightfury to save Toothless before he accepts his own impending death — it proves to be a scene nearly too harrowing and nuanced for a children’s movie as it shows the strength of the relationship between Hiccup and Toothless.

Acting quickly, the Lightfury rescues both Toothless and Hiccup, while Grimmel falls to his death. The triumphant moment quickly turns bittersweet, as Hiccup finally understands that he must accept not only the departure of Toothless, but all of the villagers’ dragons, so each one can live safely and happily in the Hidden World. The two friends exchange a heartfelt goodbye, sharing a look only each other could understand, before Toothless leads the horde of dragons toward their new home.

With the villagers returning to their old, nearly forgotten lives without dragons, Hiccup and Astrid celebrate the completion of their new village with a public wedding. While everyone celebrates Hiccup and Astrid’s marriage, the film jumps several years into the future, and Hiccup and Astrid discuss dragons with their young children as they drift across the ocean on a small ship.

As Hiccup’s tale about dragons ends, he peers into the fog to find exactly what he had been looking for — Toothless, thrilled to finally see his old friend again, with a family of his own.

The film ends with Hiccup and Astrid taking their children for their first dragon ride, before Hiccup and Toothless, reunited once more, fly together to some unknown spot in the sky.

While DreamWorks animation can often feel more cartoonish than nuanced, the “How to Train Your Dragon” series has proven to be the exception — and “The Hidden World” has only improved upon the beauty of the preceding films.

Without dialogue or human characters, the moments when Toothless meets and tries to impress the Lightfury are essentially useless to the plot, but they are some of the most touching and stunning scenes in the film because of the animation. Toothless’ charming expressions and incredible loneliness give the loveable dragon more personality than ever before, and when, for the first time in the entire series, he finally flies without Hiccup on his back, the audience is treated to a spectacular view of the world from the perspective of two lovestruck dragons.

Though the end of the film built neatly toward a climax and provided an epilogue that was both sweet and wistful, the first half suffered from uneven pacing. While significant time was dedicated to Berk, Grimmel’s initial attack on the village and Hiccup’s subsequent decision to force everyone to leave their home felt far too much like a rushed excuse to kickstart the film’s true plot: the end of Toothless and Hiccup’s relationship.

Similarly, a few of the film’s beats too closely mirrored the plots of the previous two films. In all three films, Hiccup and Toothless have a strong relationship that is threatened by an antagonistic character, they fight and Toothless is taken from Hiccup before he devises a plan to rescue his friend.

However, the repetitive quality worked both well and poorly in “The Hidden World.” The plot points themselves made the film a bit too predictable, especially when the relationship between Hiccup and Toothless was going well. Yet, scenes that mimicked moments from the first film contributed to the underlying nostalgic tone to the series finale.

The moment Hiccup’s children first met Toothless most effectively used repetition from the first film. Both Hiccup in “How to Train Your Dragon” and his children in “The Hidden World” stand in an identical stance with the same posture and bowed head before they touch Toothless for the first time. Watching a new generation of Vikings first introduce themselves to a dragon shows how much Hiccup, and the rest of Berk, has grown. In both films, it’s a powerful image, and a wonderful way to bookend the series.

Ultimately, the “How to Train Your Dragon” franchise is about friendship. For Hiccup, friendship is a team of people who support and love him, even when he believes he doesn’t deserve it. For Toothless, friendship is knowing when it’s time to let someone go. And for a generation who grew up watching “How to Train Your Dragon,” friendship is the unbreakable bond between a boy and his dragon.