Nine-year-old Ren (蓮) has recently lost his mother, whom he has lived with since his parents' divorce. With no news of his father and refusing to live with his legal guardians, Ren flees into the streets of Shibuya, resenting humanity. After stealing some food and finding an alley to sleep in, he finds a mouse to share his food with. He then reminisces about the aftermath of his mother's funeral.
In the Beast Kingdom (渋天街, jūtengai), the lord has decided he will retire in order to reincarnate as a deity and names two potential successors: the popular Iôzen, who is also the father of two children, and the powerful Kumatetsu (熊徹), who is also lonely and lazy. The Grandmaster (宗師, Shūshi) suggests that Kumatetsu find a disciple in hopes of inspiring him to succeed him.
While wandering the streets of Tokyo with his makeshift companion, Tatara(多々良), Kumatetsu meets Ren and suggests that the boy becomes his disciple. Though Ren is fiercely opposed, he follows Kumatetsu back to the Beast Kingdom out of curiosity but is unable to go back to the human world. As he watches a battle between Iôzen and Kumatetsu, Ren is impressed with Kumatetsu's persistence despite the lack of support from onlookers. When Ren cheers for him, Kumatetsu is easily defeated. However, the Grandmaster declares the actual duel of succession has not come yet.
Taking Ren as a disciple, Kumatetsu gives him a new name, Kyûta (九太 Kyūta) in relation to his age. Their initial training sessions go poorly as Kumatetsu does not know how to teach, but Kyûta realizes that he can learn from Kumatetsu by imitating him as he performs household tasks. The boy gradually finds that he can predict his master's movements to improve his fighting skills and they soon begin in training together for eight years.
Now a young adult, Kyûta has become a distinguished kendo practitioner and hopes to make his master proud. Through his relationship with Kyûta, Kumatetsu gained his own following of supporters, including the younger son of Iôzen, Jirōmaru, and receives a number of requests from young beasts wishing to be trained. By chance, Kyûta finds his way back to the human world, where he befriends Kaede (楓), a young student who helps Kyûta catch up with his studies. In the process, Kyûta finds his father, who had been searching for Ren since he disappeared and now wants to catch up on their years apart. Torn by his double life, he is unable to reconcile the resentment he had as Ren and the lack of connections he has as Kyûta. When he rejects both his father and Kumatetsu, he discovers a powerful void within himself that nearly overwhelms him until Kaede calms him down and gives him a bracelet that has helped her when she becomes anxious.
On the day of the succession duel, Kumatetsu loses confidence without Kyûta's encouragement and is nearly subdued by Iôzen (猪王山 Iōzen). However, Kyûta has been secretly watching and reveals himself, helping Kumatetsu defeat Iôzen. When Kumatetsu is declared the winner and the new lord, Iôzen's elder son Ichirôhiko (一郎彦 Ichirōhiko) is revealed to be a human who had been found on the streets of Tokyo as an infant and adopted by Iôzen. Having developed a vacuum in his heart like Kyûta, unwilling to believe that he is a human and not a beast, Ichirôhiko manifests telekinetic powers and seriously injures Kumatetsu with his own sword. Kyûta is nearly overtaken by his own emptiness and tries to kill Ichirôhiko, but regains his senses with Kaede's bracelet as Ichirôhiko is consumed by darkness and disappears.
Kyûta decides to leave for the human world to fight Ichirôhiko. When Kaede stubbornly refuses to leave him, they are attacked by Ichirôhiko, who pursues them in the form of a destructive whale. Unable to hold his own against Ichirôhiko, the young man decides to use the vacuum within himself to absorb his opponent's negative energy and then kill himself, saving everyone else. Before he can follow through with this self-sacrifice, Kumatetsu uses his new privilege as the lord and reincarnates as a deity, taking the form of a sword "to be handled with the heart" in reference to their first training session together. He merges with his pupil's form, filling his empty void within him, and guides him into defeating his enemy without killing him. Ichirôhiko wakes up surrounded by his adoptive family, understanding that he is, like Ren, a human raised by beasts, and accepts it as well.
In the aftermath, Ren celebrates his victory with Kaede in the Beast Kingdom and returns to the human world. After reconciling with his father and himself, he attends the local university and keeps Kumatetsu within his heart.
The film was released on July 11, 2015 in Japan. The film received its International Premiere at the Toronto International Film Festival and its UK Premiere at the BFI London Film Festival on October 16, 2015.
In December 2014, Gaumont secured international sales outside Asia and theatrical distribution rights in France. The film opened in select theaters in the United States on March 4, 2016. The film was released in France on January 13, 2016. Funimation has licensed the film for the US release. American theater chain AMC briefly listed the film with a February 12, 2016 opening, but later listed the film for March 4, 2016. The film has been licensed by StudioCanal for the UK and Ireland release, Madman Entertainment for the Australian release, and Mongrel Media for the Canadian release.
The film was #1 at the Japanese box office during its opening weekend by replacing Avengers: Age of Ultron, earning approximately US$5.4 million from 492,000 admissions on 457 screens, before being dethroned by Hero 2 in second week. The film was Japan's second highest-grossing film in the year 2015 with a total box office gross of (converted from yen) US$48.6 million.
The film ranked #28 at the American box office during its opening weekend on March 4, 2016. As of March 16, 2016, the film has an American box office gross of $474,308.
The review aggregation website Rotten Tomatoes reported an 90% approval rating, with an average rating of 7.5/10, based on 58 reviews. The website's critical consensus reads, "The Boy and the Beast combines familiar parts to create a gripping, beautifully animated adventure with inventive storytelling to match its visual appeal." Metacritic, which uses a weighted average, assigned a score of 65 out of 100, based on 14 critics, indicating "generally favorable reviews".
Mark Schilling of The Japan Times said that the film "has more in common with the “Harry Potter” series than the usual female-centered [Hayao] Miyazaki fantasy" and would later say that the storyline "stays centered on Kyuta’s long, vexed struggle to become not only strong, but also whole." Richard Eisenbeis of Kotaku said "[The Boy and the Beast] is an entertaining coming-of-age adventure on one hand and an excellent thematic exploration on the other. This is one of those films that is perfect for any age group—there’s something for everyone in this one" Charles Solomon of the Los Angeles Times said "'[The] Boy and [the] Beast' is a bracing tale of two flawed individuals who find the love and discipline they need to assume their rightful places in their respective worlds." Peter Debruge of Variety called it, "an action-packed buddy movie that strategically combines several of Japanese fans’ favorite ingredients: conflicted teens, supernatural creatures and epic battles." Peter Keough of The Boston Globe gave the film 2.5 out of 4 stars and wrote, "[Hosoda] does know how to mix an eclectic array of film plots and concepts into a mish-mash that seems original." Pat Padua of The Washington Post wrote, "But it is the world of man, not beast, that makes this coming-of-age movie most touching."
Andy Webster of The New York Times was more critical of the film, saying "Mr. [Mamoru] Hosoda is skilled with fight scenes, and his settings — the pastel-hued Jutengai and the drab Shibuya, evoked at times with surveillance-camera perspectives and crowd-paranoia angles — are impressive. But the characterizations and conflicts here are strictly generic." Sherilyn Connelly of The Village Voice said that the film "works with many common anime tropes but doesn't find anything new to say about them." Marc Savlov of The Austin Chronicle gave the film 2.5 out of 5 stars and said "A huge success in Japan, this thrilling, if overlong, epic from director Mamoru Hosoda (Wolf Children, Summer Wars) is part Karate Kid and part Japanese folklore." Jacob Chapman of Anime News Network had a mixed response to the film and said "The Boy and The Beast is the kind of movie you put on to please a kid with its loudness and color, but promptly leave the room to do something else.