"Eiga Ojarumaru Yakusoku no Natsu Ojaru to Semira" is a feature-length anime film based on the long-running children's series "Ojarumaru." The story centers on Ojarumaru, a mischievous young prince from the Heian period who, after being banished from his kingdom, finds himself in modern-day Japan. Accompanied by his loyal companions, the trio of oni demons—Denbo, Suzume, and Akane—Ojarumaru navigates the challenges of adapting to contemporary life while retaining his regal demeanor and penchant for causing chaos.

The narrative unfolds during a summer vacation, where Ojarumaru and his friends encounter Semira, a mysterious girl with a connection to the supernatural. Semira possesses a magical flute that holds the power to control time, a relic tied to her tragic past. As Ojarumaru becomes entangled in Semira's quest, the group embarks on an adventure to uncover the truth behind the flute's origins and its potential to alter the course of history. Along the way, they face various obstacles, including rival spirits and the looming threat of time itself unraveling.

The film explores themes of friendship, responsibility, and the consequences of wielding power. Ojarumaru's growth is central to the story, as he learns to balance his playful nature with the gravity of the situation. Semira's character adds emotional depth, as her backstory reveals a longing for redemption and a desire to right past wrongs. The dynamic between the characters drives the narrative forward, blending humor, heartwarming moments, and lighthearted action.

The plot is structured around a series of episodic adventures that gradually build toward a climactic confrontation, where the true nature of the flute's power is revealed. The resolution emphasizes the importance of making amends and cherishing the present, tying together the film's central themes. The film maintains the whimsical tone of the original series while introducing a more expansive and emotionally resonant storyline, making it accessible to both longtime fans and newcomers.