On a distant battlefield, a fierce clash unfolds on a faraway planet, and the planet’s president is evacuated in a rocket before the battle gives way to a shift in fate. The scene then cuts to Earth, where Nobita Nobi [(/actor/noriko-ohara)] is kicked out by Gian [(/actor/kazuya-tatekabe)] and Suneo Honekawa [(/actor/kaneta-kimotsuki)] after wrecking the makeshift space-set they’re shooting. He races to Doraemon [(/actor/nobuyo-oyama)], and the two enlist Shizuka Minamoto [(/actor/michiko-nomura)] to help them craft their own film, turning a moment of trouble into a shared project.
During the filming, Nobita stumbles upon something that looks like a toy rocket, and later that night, he and Doraemon discover a tiny, smart humanoid alien named Papi [(/actor/keiko-han)] hiding in their room. Papi explains that a dangerous pursuer is after him, and Nobita, Doraemon, and Shizuka assure him he’ll be safe at home. To play along, they all shrink to Papi’s size with Doraemon’s Small Light, slipping into a world where even ordinary objects become portals to adventure.
Meanwhile, trouble intensifies when a whale-shaped battleship destroys Suneo’s new set, and Suneo and Gian confront Nobita at his house. Papi reveals that the attacker was sent by PCIA, an organization whose mission is to capture him, because Papi is the president of Pirika, a planet now under the rule of the dictator Gilmore [(/actor/yusaku-yara)]. PCIA’s goal is to ensure Gilmore’s total victory, and the stakes grow as Nobita and friends realize the danger Papi faces.
To protect him, the children hide Papi in a secret base tucked away inside Shizuka’s home, crafted with Doraemon’s gadgets. But the PCIA battleship infiltrates the base, kidnapping Shizuka and stealing the Small Light, preventing the kids from returning to their normal sizes. Dorakoruru, the head of PCIA [(/actor/nobuo-yana)], leaves a chilling ransom note demanding Papi in exchange for Shizuka’s life.
Undeterred, Papi sets out to surrender while the others improvise, altering Suneo’s model tanks to become capable of flight and combat. Rokoroko, Papi’s loyal dog [(/actor/yuji-mitsuya)], arrives in time but cannot save him, and the dog and Shizuka eventually rejoin the group. Together they decide to travel to Pirika using the same rocket that first carried Papi to Earth, hoping to find safety and a chance to rally resistance.
Approaching Pirika, Nobita and friends reach a hidden base located in the planet’s ring, where Army chief Genbu explains that Papi is held at the PCIA head office and faces a death sentence. Doraemon, Nobita, and Gian head to the planet with Rokoroko, while Shizuka and Suneo stay behind to defend the base. They encounter a resistance group, but PCIA soldiers locate and capture them through Gilmore’s surveillance. After landing on Pirika’s surface in tanks, Shizuka and Suneo are shot down; their tanks sink, and they revert to their normal sizes.
Back at the PCIA headquarters, Nobita, Doraemon, Gian, Papi, and Rokoroko stand at the edge of execution, only to be interrupted by news that giant Earthlings have appeared. With the Small Light’s effects expired, the trio returns to their normal sizes and reunites with Shizuka and Suneo just in time to mount a counterattack. Dorakoruru battles in a PCIA battleship, but Gian single-handedly brings it down, sending the vessel crashing into the ocean. Gilmore attempts to flee, yet a crowd of Earthlings surrounding him forces a surrender.
In the end, Nobita and friends bid farewell to Pirika’s residents and begin their journey home to Earth, talking warmly about visiting Pirika again soon. The ending credits flash with snippets of their future visits, hinting at new adventures and continued friendship across worlds.
