"Soreike! Anpanman: Niji no Pyramid" 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 revolves around a mysterious rainbow-colored pyramid that appears in the sky, causing a series of unusual events. The pyramid is revealed to be the work of Baikinman, a recurring antagonist, who seeks to harness its power to spread chaos and darkness.

Anpanman, along with his friends such as Shokupanman, Currypanman, and Melonpanna, embarks on a journey to uncover the secrets of the pyramid and stop Baikinman's plans. The pyramid is not only a source of immense energy but also a gateway to a parallel world where the characters encounter new allies and face unexpected challenges. The narrative explores themes of teamwork, courage, and the importance of helping others, as the heroes work together to restore balance and protect their world from Baikinman's schemes.

The film introduces new characters, including a mysterious girl named Niji-chan, who is connected to the pyramid and plays a pivotal role in the story. Her presence adds depth to the plot, as her origins and abilities become central to resolving the conflict. The story also delves into the dynamics between the main characters, highlighting their unwavering dedication to justice and their willingness to sacrifice for the greater good.

As the plot unfolds, the heroes face a series of trials within the pyramid, each designed to test their resolve and unity. The climax involves a dramatic confrontation with Baikinman and his minions, culminating in a battle that determines the fate of both worlds. The resolution emphasizes the enduring values of kindness and perseverance, reinforcing the core messages of the "Anpanman" series. The film maintains a balance of action, humor, and heartfelt moments, making it an engaging addition to the franchise.