In a post-ice age Alaska, local tribes hold a belief that all living beings are manifestations of the Great Spirits, who reveal themselves through the aurora. An elderly man named Denahi recounts a significant tale involving him and his brothers to his tribe. The story revolves around three brothers: Kenai (the youngest), Denahi (the middle), and Sitka (the eldest), who return to their tribe so that Kenai can receive his totem from Tanana, the tribe's shaman. Each brother's totem, in the form of distinct animal necklaces, symbolizes the qualities they must embody to achieve manhood.
In contrast to Sitka, who is bestowed the eagle of guidance, and Denahi, who receives the wolf of wisdom, Kenai is given the bear of love. He vehemently objects to this totem, believing bears to be thieves and unintelligent creatures devoid of emotion. His belief is seemingly validated when a brown bear steals their basket of salmon. In an attempt to retrieve the basket, Kenai encounters the bear and provokes it. This confrontation culminates in a battle atop a massive glacier. As the bear gains the advantage, Sitka heroically sacrifices himself to save his younger brothers by dislodging the glacier, although the bear manages to survive the fall. Following Sitka's funeral, a furious Kenai blames the bear for his brother’s death, leading him to reject his totem. He then pursues the bear onto a cliff, where he engages in a fierce struggle and ultimately kills it.
However, the Great Spirits, embodied by Sitka's spirit appearing as a bald eagle, intervene, transforming Kenai into a bear as the deceased bear's body dissipates into their realm. Denahi mistakenly believes that Kenai was slain by the bear. After a harrowing fall, Kenai survives the plunge into rapids and regains consciousness, only to find that he is now in the form of a bear. Unable to communicate with him, Tanana advises Kenai to travel to the mountain where the lights touch the earth to reunite with Sitka and regain his human form—only after he atones for his misdeeds.
As Kenai navigates his new life, he discovers that he can understand the local wildlife, including a pair of comedic moose brothers, Rutt and Tuke. He initially finds himself caught in a trap but is rescued by an adventurous bear cub named Koda. After a narrow escape from Denahi, Koda shares that his mother has gone missing. They strike a deal: Kenai will guide Koda to the annual salmon run, after which Koda will lead Kenai to the mountain. During their journey, a brotherly bond forms between Kenai and Koda, further enriched by their encounters with Rutt and Tuke and even a herd of wooly mammoths. However, they press forward on foot, with Denahi relentless in his pursuit, seeking vengeance for what he believes to be Kenai's death.
Arriving at the salmon run, Kenai is embraced by a community of bears, including their leader, Tug. Adapting to this new environment, Kenai enjoys the company of other bears. During a storytelling session, Koda recounts a tale of his mother clashing with human hunters on a glacier, striking a painful chord with Kenai, who realizes that Koda's mother is the bear he killed. Overwhelmed by guilt, Kenai flees, causing Koda to follow, heartbroken by the truth of his mother's fate.
Meanwhile, Rutt and Tuke's reconciliation inspires Koda to forgive Kenai. In a climactic confrontation atop the mountain, Kenai faces Denahi but their altercation is abruptly halted when Koda intervenes, seizing Denahi's spear. Motivated by love, Kenai leaps to protect Koda, drawing forth Sitka’s spirit, who transforms him back into a human, shocking both Denahi and Koda alike. However, recognizing that Koda needs him, Kenai convinces Sitka to revert him back to a bear, with Denahi's understanding. Sitka complies, and once again, Kenai becomes a bear. Koda briefly reunites with his mother's spirit before she and Sitka return to the spirit world.
In conclusion, Kenai chooses to remain with the bear community and earns his title as a man through his actions as a bear. The elderly Denahi concludes the tale with an important message about the boundless power of love.
