The film opens with Morina and Roppuru playing in a park aboard a spaceship, sharing a moment of innocent curiosity as they explore a strange, floating world. An abrupt earthquake shakes the vessel, freezing the ship in place, and Morina’s father works tirelessly to repair it. Just as his efforts seem to bear fruit, a bolt of lightning strikes, and tragically, he is presumed dead, leaving the siblings and their crew to contend with the sudden loss and the uncertainty that follows.
Back on Earth, Nobita wakes up convinced that what he just witnessed was all a dream. Doraemon appears with a calm, knowing voice and informs him that Gian and Suneo are searching for him. The three boys become entangled in a scheme to secure an empty lot from a group of middle school baseball players, but the plan spirals out of control when the players pursue Nobita, and he is knocked unconscious in the clash. This sequence blends humor with tension, hinting at how quickly friendship and mischief can collide with real danger.
Nobita drifts into another dream where Roppuru and Chammy attempt to outrun capture by a menacing ship. Upon awakening, the rest of the group urges Doraemon to conjure land large enough for a baseball stadium, a proposal that Nobita and Gian reluctantly agree to entertain, even if their reservations are clear. The promise of progress clashes with the sense that they are stepping into something larger than themselves, a feeling that threads through the subsequent adventures.
While Nobita sleeps again, tremors rumble beneath him, and Chammy forces a door between their spaces open. Nobita wakes Doraemon, and the pair catch Chammy in the act of stealing food from a refrigerator. They pursue Chammy through a labyrinth of hallways and passages, and after a tense chase, they capture her. Chammy then reveals a hidden passageway that leads directly into the spaceship. They venture inside, repair what is broken, and set course for home, the ship humming with a fragile, tentative hope.
The sense that they might have finally returned home is short-lived. Nobita and Doraemon worry that their experiment last night may have stranded them in another dimension once again, so they attempt the passage anew and end up far from familiar skies. They soon encounter Roppuru’s family and Morina, who remains cool and distant at first, yet they quickly realize something crucial: the spaceship itself has vanished. When it is eventually located, the group resolves to bring their friends along on the next attempt, determined to uncover the truth behind the disappearance.
The following day, Nobita gathers his friends to revisit the strange planet, only to be attacked by mining agents intent on extracting resources from the surface. The ambush forces the group to flee back to their own dimension, fracturing their sense of safety and making them aware that a greater corporate force is at work. As Dorami accompanies Doraemon to a medical checkup, Nobita attempts to strike out on his own and is pulled into another dimension, landing on yet another world where an unseen pursuer closes in before a sudden gadget from Doraemon saves him.
In their next encounter, Nobita and Doraemon clash again with the mining faction, their ship overwhelmed in battle. Roppuru’s town learns of the strange events, but crucial evidence is taken away by the miners, leaving authorities with little to show. The mounting danger prompts Guillermin, a cunning antagonist, to step in and devise multiple schemes to disable Nobita and Doraemon, testing their ingenuity at every turn. Each plan fails, pushing the conflict toward a higher-stakes finale.
Doraemon and Nobita decide they cannot stay away forever, and word reaches Morina that the situation is escalating. Guillermin presses Morina for information about her father’s death, hinting at a buried truth that stretches back to the planet’s history—truths that complicate loyalties and blur the lines between ally and adversary. Meanwhile, agents tamper with a dimensional door by attaching a bomb that could obliterate anyone who attempts to open it. Nobita’s mother, ever protective, scolds him for staying out late and urges him to remain in his room.
When the team finally attempts to reopen the dimensional door, the explosive device detonates, leaving the ship damaged and in ruins, though the group narrowly survives the blast. The people of Koya Koya are ordered to evacuate the planet as the mining corporation prepares to blow it up and seize control. Chammy and Clem recover the dimensional door, while Morina and Roppuru work to piece together what is truly happening behind the curtain of corporate greed and interdimensional travel. Chammy enters Nobita’s room, and together with Nobita and Doraemon, they plunge back inside to search for Roppuru, with Nobita’s friends and Dorami following, knowing that this will likely be their last chance to enter.
The journey culminates in a dramatic confrontation where Doraemon, Nobita, and their allies cut through interference and face Guillermin in a decisive duel. The detonation button is pressed, and the uppermost echelons of power scramble to escape the scene. In a bold, coordinated effort, Doraemon, Nobita, Roppuru, and Morina deploy a robotic mechanism to haul the dangerous device away from the planet and into a separate dimension, where it detonates in a final blaze of energy.
Warping through dimensional distortions, Morina finds herself slipping into another dimension and reunites with her father, who appears to have resided there all along. The film closes on a note of bittersweet farewell as the characters reflect on the experiences they shared and the friendships that carried them through the perilous voyage, leaving Nobita and Doraemon to ponder the lessons of resilience, teamwork, and the sense that exploration—whether spacebound or dimensional—often changes a person forever on a planet they barely knew.
