"Pikachu no Natsumatsuri" is a short anime special centered around Pikachu and its friends as they prepare for and participate in a summer festival. The narrative begins with Pikachu and its companions, including Piplup, Bulbasaur, and Charmander, working together to set up decorations and stalls for the festival. The group is excited about the event, which promises games, food, and fireworks. However, their preparations are interrupted when a sudden storm threatens to ruin the festivities.

As the storm approaches, the Pokémon must work together to protect their hard work and ensure the festival can proceed. Pikachu takes on a leadership role, coordinating efforts to secure decorations and keep the festival grounds safe. The storm intensifies, creating tension as the Pokémon face challenges such as strong winds and heavy rain. Despite the difficulties, their teamwork and determination shine through as they manage to overcome the obstacles.

The climax of the story occurs during the festival itself, where the Pokémon and their human friends come together to celebrate. The storm clears, and the night sky is illuminated by a spectacular fireworks display, symbolizing the success of their efforts. The special concludes with a sense of camaraderie and joy, highlighting the bonds between the Pokémon and their shared love for the summer festival.

The main characters include Pikachu, who serves as the central figure, and its friends Piplup, Bulbasaur, and Charmander, each contributing their unique abilities and personalities to the group. The story emphasizes themes of teamwork, perseverance, and the joy of community celebrations, making it a lighthearted and engaging watch for fans of the Pokémon series.