"Eiga! Tamagotchi Uchū Ichi Happy na Monogatari!?" is a feature-length anime film based on the popular Tamagotchi franchise. The story centers on Mametchi, a cheerful and curious Tamagotchi character, and his friends as they embark on an interstellar adventure. The narrative begins when Mametchi discovers a mysterious spaceship in his backyard, which leads him and his friends—Memetchi, Kuchipatchi, and Lovelitchi—to travel across the universe. Their journey takes them to Planet Tamagotchi, a vibrant world inhabited by various Tamagotchi characters.

Upon arrival, the group learns that Planet Tamagotchi is in danger due to a looming threat from a dark force that seeks to drain the planet's happiness. The main characters must work together to restore joy and harmony to the planet. Along the way, they encounter new allies, including the enigmatic Spaceytchi, who provides guidance and support. The story emphasizes themes of friendship, teamwork, and perseverance as the characters face challenges and uncover the true source of the planet's distress.

The plot unfolds through a series of episodic adventures, each highlighting the unique traits and contributions of the main characters. Mametchi's intelligence and problem-solving skills, Memetchi's creativity, Kuchipatchi's humor, and Lovelitchi's compassion all play pivotal roles in overcoming obstacles. The film culminates in a climactic showdown where the characters must confront the dark force and use their collective strengths to save Planet Tamagotchi. The resolution reinforces the importance of unity and the power of happiness in overcoming adversity.