In a mystical forest brimming with life, unicorns coexisted peacefully with wild animals. However, everything changed when a group of bears stumbled upon a sacred text hidden in the ruins of an ancient church. This forbidden book granted them the ability to think and feel like humans, allowing them to establish their own civilization. Over generations, the bears transformed into vibrant, teddy bear-like creatures. Driven by a desire to nurture the forest, their intentions were met with hostility from the unicorns, who were ultimately forced to retaliate against the bears' destructive deforestation campaign. As a result, war erupted, igniting a fierce conflict where the bears believed it would culminate in their "chosen one" drinking the blood of the last unicorn, thus summoning a god-like entity back to their realm.
Within this turbulent backdrop, Drill Sergeant Caricias, portrayed by Manu Heras, trains a fresh cohort of recruits, including brothers Gordi and Azulín, played by Jaione Insausti and Jon Goiri, respectively. As the soldiers undergo rigorous training, a priest teaches them a dogma steeped in hatred for unicorns. Eager to impress and protect his brother, Azulín harbors aspirations of becoming the Chosen One. However, his feelings of jealousy towards the top recruit, Coco, begin to consume him. This envy is compounded by his long-standing resentment towards his brother, who was born first and swiftly captured their mother’s affection. When their mother chose to leave their father for another man, Azulín's jealousy escalated to a nightmarish climax, leading him to poison her lemonade and inadvertently take her life.
The military leaders send the troop on a mission to locate a missing squad in the depths of the forest, guided by Sergeant Caricias and the Priest. Amidst the trees, they discover bioluminescent glowworms that they contemplate eating. Ignoring the Priest's warnings based on scripture, Sergeant Caricias’s defiance results in disastrous consequences, as the glowworms prove to be hallucinogenic, leading to horrific visions that claim the lives of two recruits. Eventually, they stumble upon the dismembered remains of their missing comrades. The psychological strain drives Sergeant Caricias to madness. Soon, they come across a lone unicorn and, in a fit of rage, kill her. However, this act provokes a fierce fight with other unicorns, leaving only Azulín, Gordi, and Coco as survivors. In a moment fueled by blind rage, Azulín slays a wounded Coco, even resorting to cannibalism.
The brothers then encounter two unicorns, resulting in a brutal confrontation where Azulín severely injures a filly named María, while the other unicorn, Laura, impales him in retaliation, casting him into a river and causing horrific disfigurement on the right side of his face. Rescued by a separate troop consisting of Corporal Pompon, Private Peludito, and Private Grimaldo, Azulín receives medical care. After his recovery, military leaders Colonel Otto, Commander Fluffy, and Captain Snout appear, decorating him as a hero and even promoting him to Lieutenant, presenting him with a mask that conceals his scars. Meanwhile, Gordi shows compassion for María, nursing her back to health, bringing hope amidst the chaos.
As Azulín’s reputation swells within the ranks, he stages a violent coup, eliminating his superiors, and assembles the bear army for one final annihilative assault on the forest. All unicorns rally together against the impending threat of the bears. In a horrific final confrontation, the battle claims the lives of nearly all bears and unicorns, leaving only Azulín and Gordi alive, alongside María. Yet, when Azulín witnesses Gordi tending to María, his rage erupts once more, leading to the brutal slaying of both Gordi and María. Consumed by the prophecy, Azulín drinks María's blood, triggering her transformation into a monstrous being that ultimately devours both brothers. In the finale, this fearsome entity morphs into a human figure, heralding the rise of the simians as the new overlords of the world.
