Pua is first seen as part of Moana's childhood during "Where You Are". From there, he acts as Moana's sidekick and confidante throughout both her daily routines as the soon-to-chief of Motonui and her downtime. Moana feels pulled to the sea despite her father's law that forbids anyone from leaving the island. Pua, however, supports Moana and feels saddened whenever she's forcibly distracted from her apparent calling.
When the island falls under a curse that slowly destroys their food supply, Moana believes the only solution is to go beyond the island's barrier reef to find food elsewhere. Tui forbids this, prompting Moana and Pua to go out alone. The further out they go, the more dangerous the waters become. Soon enough, the boat is struck by a powerful wave that nearly drowns both Moana and Pua. They manage to make it to the shore, but the experience traumatizes Pua so much that the mere sight of Moana's oar causes him to run back to the village in fear. When Gramma Tala sees the damage, she playfully advises Moana to blame it on Pua.
Pua is not seen again until the very end of the film, where Moana returns home from her quest to save the island. As she embraces her parents, the villagers come to greet her, with Pua being the most excited to reunite with his friend. During the finale reprise of "We Know the Way", Pua is seen sailing with Moana and her family (with Heihei atop his head) as they revive their island's voyaging roots.
Spoilers end here.
Pua's name is derived from the word "puaka", which refers to "pig" and "pork" in some Polynesian languages.
As seen in the marketing campaign and early footage, Pua was originally going to join Moana on her adventure. As the story developed, however, he was cut, and instead remained on Motunui as Moana journeyed off.
The story team joked that co-director Ron Clements is the persona of Pua.
Pua was originally going to appear in the third installment of Disney INFINITY as a mount. This never saw fruition, as the series was cancelled before the Moana playset was released.