Watch The Boy and the Beast

Nine-year-old Ren has recently lost his mother, whom he has lived with since his parents divorced. With no news of his father and refusing to live with his legal guardians, Ren flees into the streets of Shibuya filled with hatred for humanity.
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, who is also lonely and lazy. The Beast Lord (バケモノ, bakemono) 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, 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 finds he cannot 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 surprised and distracted, leading to his defeat. However, the Beast Lord declares actual duel of succession has not come yet.

Kumatetsu decides to take Ren as a disciple and gives him a new name, Kyûta in relation to his age (Kyuu (九) means nine in Japanese). 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 in harmony.

Eight years later, Kyûta, now a young man, 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, and receives a number of requests from young beasts wishing to be trained. By chance, Kyûta finds his way back the human world, where he befriends Kaede, a young student who helps Kyûta catch up with his studies. In the process, Kyûta discovers that his father is hoping to meet him and catch up on their lost years apart. Torn by his double life, he is unable to reconcile the hatred he had as Ren and the lack of connections he has as Kyûta. When he rejects both his father and Kumatetsu, he uncovers 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 quickly overwhelmed by Iôzen. However, Kyûta has been secretly watching and reveals himself, providing the support and advice Kumatetsu needs to overcome Iôzen. When Kumatetsu is declared the winner and the new lord, Iôzen's elder son Ichirôhiko is revealed to be a human who had been found on the streets of Tokyo and adopted by Iôzen. Having developed a vacuum in his heart like Kyûta, Ichirôhiko manifests telekinetic powers and deeply injures Kumatetsu. Enraged and griefstriken, 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 and save everyone else. However, 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.

After attending a celebration in their honour with Kaede in the Beast Kingdom, Ren decides to return to the human world. After reconciling with his father and himself, he attends university and keeps Kumatetsu within his heart. Meanwhile, Ichirôhiko wakes up surrounded by his adoptive family, understanding that he is, like Ren, a human raised by beasts, and accepts it as well.

The Boy and the Beast is a 2016 action movie with a runtime of 1 hour and 59 minutes. It has received mostly positive reviews from critics and viewers, who have given it an IMDb score of 7.6 and a MetaScore of 65.