Jirohmaru is a supporting character in the anime film The Boy and the Beast. He is the younger son of Iouzan, the wise and powerful lord of the beast realm.

As a child, Jirohmaru’s worldview is simple and straightforward, placing value almost entirely on physical strength. He initially bullies the human boy Kyuta, looking down on him for being weak. This attitude changes immediately after Kyuta defeats him in a minor scuffle, as Jirohmaru is impressed and quickly warms up to him, turning a rivalry into a friendship. He has a thick, brown unibrow, and as a teenager, he sports a prominent pomp hairstyle.

Jirohmaru’s motivations are largely tied to his admiration for strength and his family. He greatly admires the power of his older brother, Ichirohiko. While he starts as something of a bully, he mellows out considerably as he grows, becoming a friendly and more easygoing individual. His role in the story is primarily as a supporting figure to Kyuta and as a foil to his brother. After a time skip in the narrative, the dynamic between the brothers shifts. Jirohmaru becomes more respectful and balanced, treating both his father and Kumatetsu, Kyuta's master, with equal regard. In contrast, Ichirohiko grows more bitter and arrogant. Even after witnessing his brother’s corruption and learning about Ichirohiko’s origins as a human who was adopted, Jirohmaru’s loyalty does not waver. He firmly maintains that they are still brothers, regardless of what anyone else thinks. Jirohmaru does not possess any notable supernatural or combat abilities that are unique from other beast folk in the film.