"Soreike! Anpanman: Happy no Daibōken" is a feature-length anime film based on the popular "Anpanman" franchise, which centers around the adventures of Anpanman, a superhero made of anpan (a sweet bread filled with red bean paste). The story begins with Anpanman and his friends living in a vibrant, whimsical world where they protect the innocent and spread happiness. The narrative takes a dramatic turn when a mysterious spaceship crashes near their home, bringing with it a new character named Happy, a cheerful and energetic alien.

Happy quickly befriends Anpanman and his companions, including Baikinman, a mischievous antagonist who often causes trouble but occasionally aids the heroes. Happy reveals that his home planet, Happy Star, is under threat from a dark force known as the Shadow King, who seeks to engulf the universe in darkness. Determined to save Happy Star and restore light to the galaxy, Anpanman and his friends embark on a daring interstellar journey.

The group faces numerous challenges as they travel through space, encountering strange planets, alien creatures, and the Shadow King's minions. Along the way, they learn the importance of teamwork, courage, and kindness. Anpanman's ability to share pieces of his head, made of anpan, to feed those in need becomes a recurring theme, symbolizing selflessness and compassion. The film balances lighthearted moments with high-stakes action, as the heroes confront the Shadow King in a climactic battle to save Happy Star and the universe.

The main characters include Anpanman, the selfless and brave protagonist; Baikinman, the unpredictable yet resourceful antihero; and Happy, the optimistic alien whose plight drives the central conflict. Supporting characters such as Shokupanman, Currypanman, and Melonpanna contribute to the group's dynamic, each bringing unique abilities and personalities to the adventure. The film's narrative emphasizes themes of friendship, resilience, and the power of hope, making it a fitting addition to the "Anpanman" series' legacy of uplifting storytelling.