"Soreike! Anpanman: Anpanman to Happy O-Tanjōbi" is a special installment in the long-running "Anpanman" franchise, which centers on the adventures of Anpanman, a superhero whose head is made of anpan (a sweet bread filled with red bean paste). The story revolves around a celebration of a character's birthday, emphasizing themes of friendship, kindness, and community.

The narrative begins with Anpanman and his friends preparing for a joyous birthday celebration. The atmosphere is filled with excitement as they decorate, bake cakes, and plan surprises. However, the festivities are interrupted by Baikinman, a mischievous antagonist who thrives on causing trouble. Baikinman, along with his sidekick Dokin-chan, devises a plan to ruin the birthday party, aiming to spread chaos and unhappiness.

As the story unfolds, Anpanman and his friends, including Shokupanman (a bread superhero with a loaf of bread for a head) and Currypanman (a curry-filled bread hero), work together to thwart Baikinman's schemes. The heroes use their unique abilities and teamwork to protect the celebration and ensure that the birthday remains a happy occasion. Along the way, they encounter various challenges, including traps set by Baikinman and moments of doubt, but their determination and camaraderie ultimately prevail.

The central theme of the story is the importance of kindness and the joy of giving. Anpanman, known for his selflessness, often sacrifices parts of his own head to feed those in need, symbolizing generosity and care. This act of giving is highlighted during the birthday celebration, reinforcing the idea that happiness is best shared with others. The narrative also underscores the value of friendship, as the characters come together to support one another and overcome obstacles.

The special maintains the lighthearted and educational tone characteristic of the "Anpanman" series, making it accessible to its primary audience of young children. The characters' interactions and the resolution of conflicts are presented in a straightforward manner, emphasizing positive moral lessons. The story concludes with the successful celebration of the birthday, leaving the characters and viewers with a sense of fulfillment and joy.