Shortly after the pilot episode, Unico: Black Cloud and White Feather in 1979, production for a theatrical release of Unico began. Toshio Hirata would direct the film while Shintaro Tsuji (founder and chairman of Sanrio) and Susumu Aketagawa (producer of the pilot episode) asked Madhouse to produce the animation instead of Sanrio's in-house animation department. They made the movie similar to Disney films, using not the usual 12 frames per second, but 24 frames, creating a smoother animation. Osamu Tezuka was still busy with other works, but could supervise the movie's production.
Masaki Tsuji wrote the movie's script which included two of the manga's chapters: "The Cat on the Broomstick" (Houki ni Notta Neko) and "Unico and Solitude" (Hitoribocchi no Yuniko) with changes to create a full-length movie.
Folk singer Iruka provided narration and songs for the movie while the ending theme, "Love is Everything" (Ai koso subete), is provided by BUZZ (& Sumie Shima).
The movie premiered in Japanese theaters close to springtime on March 14, 1981, along with the stop-motion short, "Kitty and Mimmy's New Umbrella." Unico gained popularity in many countries across the globe and has been dubbed in several languages. They made plenty of merchandise during this time and Sanrio's newspaper, The Strawberry News (Ichigo Shinbun), had a special issue featuring information and images of products.
The manga was also re-released toward the end of 1981 in two volumes known as the Ai no Bouken (Adventure of Love) set. Similar to the special editions put out by Sanrio in the late 70s, the Ai no Bouken set featured large colored pages.
The movie opens with a musical intro about who Unico is and how he brings happiness to those who are kind to him. A group of elder gods, angry with the little unicorn's abilities, end up deciding Unico's fate. Unico would be expelled to the Hill of Oblivion at the ends of the earth, far away from anyone.
The West Wind and Unico travel a great distance, but she cannot bring him to the Hill of Oblivion. Instead, she leaves him on a desolate island in hopes the gods would not notice. When Unico awakes, he cannot remember anything and is extremely lonely. He spots a castle in the distance and is filled with determination. Upon reaching the castle, he only finds a massive statue of the Devil of Solitude. When Unico tries to befriend Solitude, the statue sends down bolts of lightning to scare Unico away. The lightning hits a large pillar which falls onto the statue, demolishing it.
After the disaster, Unico hears crying from the rubble and investigates. He finds an upset devil child, angry with Unico for destroying his father's statue. Despite everything, Unico still tries to befriend the little devil, promising to give him whatever he wants if he'll be his friend. Akuma-kun wants Unico's horn and while Unico is reluctant to do so, he finally agrees but only if he'll promise to give it back after one day. The devil agrees and Unico's horn comes off and attaches to Akuma-kun's head without an issue.
Akuma-kun is excited and when he plays with Unico, he is very rough. He chases Unico to a cliff and Unico falls off and into the ocean. When he cries for Akuma-kun to help him, the little demon doesn't understand the meaning of "help" and returns to the castle.
Time goes by and Akuma-kun grows impatient, knowing he has to keep his promise to Unico. In the end, the demon child leaps into the ocean to give Unico back his horn, saving his life. Unico realizes the demon sacrificed his life to return the horn, so Unico saves him, granting him his own horn as well. West Wind soon appears for Unico and takes him far away once more, leaving the little devil alone on the island.
When Unico arrives in a flowery field, he meets the black and white cat named Chao riding in a basket down the river after being abandoned by her previous family. Together, they venture off and find a cottage in a forest clearing. Chao's wish is to become a witch and when an elderly woman saunters in, she immediately believes she's a witch and will teach her how to be one.
Before falling asleep, Chao mentions wanting to become a real girl and Unico wants to make her wish come true. While the elderly woman is hanging linens out to dry the next day, one falls on top of Chao. Unico uses his magic to turn her human, and she's able to put the sheet back up. She finally realizes what's happened to her and believes the old woman transformed her.
It surprised the elderly woman to see a young girl at her home, but she welcomes the companionship and help Chao provides. Unico also enjoys seeing Chao help the woman, but when Chao complains about the chores, she wanders off. Unico tries to reason with her, explaining that the old woman needs the help. He turns Chao back into a cat and she quickly grows upset. Unable to transform back, Chao remains by the lonely older woman's side.
While washing linens by the river, the old woman falls into the water while trying to grab a cloth that had fallen in. Unable to swim, the woman struggles to stay above the surface. Without thinking, Chao leaps into the water to save the old woman, her body transforming back into a human.
While by the river to gather water, Chao meets an attractive yet mysterious man on a horse named Baron Ghost. He invites her to his castle, ordering her to come alone and to tell no one. Chao agrees, easily twitterpated by the man and not questioning his motives. After he leaves, Chao is smitten and accidentally falls into the river.
During the night, Baron rides through the forest on horseback, casting a spell on the nuts and berries. The animals eat the fruit and their eyes glow green, now controlled by the wicked man. By morning, the sun is bright, and Chao is excited to head out to the Baron's castle. When questioned by Unico, she lies to him, but he still warns her to not go out into the forest. An injured animal is nearby, and while Unico is attending to it, Chao slips away.
In the forest, Chao spots a bunch of berries on a bush and helps herself. The berries instantly place Chao in a drunken state, and she wanders the forest. The forest comes to life, leading her toward the castle. When she arrives and enters, she's amazed by the massive entryway. Baron greets Chao and she's completely enamored, unable to sense any danger.
Meanwhile, Unico is running through the forest, searching for Chao. The forest tries to prevent Unico from coming any closer to the castle, but he's able to get through. He spots Chao sitting at a table with the Baron, now drunk from the wine he's given her. After she passes out, Baron places her on a bed. Unico works quick, causing a distraction by jumping on the organ keys. The Baron rushes out to investigate and Unico dashes off to save Chao.
Unico sneaks Chao out of the castle, but Baron Ghost finds them before they get far. Baron and Unico fight for a moment, but once the Baron's sword is snapped, his eyes glow and they knock Unico back. As Unico falls unconscious, the Baron kidnaps Chao back to his castle.
We now see ocean waves crashing against an island with Akuma-kun on a ledge. West Wind is flying by, and he spots her. She appears before him and says Unico is in danger. Together they head toward Unico's location but are met with the troublesome Night Wind who tries to stop them. They get away and spot Unico in the forest. Upon reuniting, Akuma-kun and Unico work together to save Chao. Unico attacks the Baron, who allows himself to be cut by Unico's horn, and he plummets down, only to be impaled on a spire. The Baron is not dead yet, instead he transforms into a Great Devil, wielding a massive axe.
Akuma-kun, Chao, and Unico run for safety as the Great Devil destroys the ground below them, forcing lava to spew to the surface. The Great Devil still controls the forest and forces the trees to attack the three. The three fought their way out and find safety from the lava that now has covered much of the land.
Not wanting his friends or the other animals in the forest to be hurt, Unico flies off to deal with the Great Devil. Dodging lightning, attacks from summoned bats, and the Great Devil's jaws, Unico tries his best to fight. With one swing, the Great Devil breaks Unico's horn with its axe and Unico falls to the ground. Chao and Akuma-kun rush to their friend's lifeless body. While Chao sheds tears that fall on Unico, Akuma-kun gives Unico his horn and he transforms into his adult form.
Unico, now rejuvenated, flies into the sky and pierces through the Great Devil, forcing it back into the depths of the earth. The animals return and everyone is happy once more except Unico. The West Wind comes for Unico and takes him away once more.