Nobita Nobi is a Fifth grader who constantly gets failing grades in his subjects due to his laziness and is always bullied by his classmates Suneo Honekawa and Takeshi “Gian” Goda. His great-great grandson from the 22nd century, Sewashi, who watches him every day, travels to Nobita’s timeline while bringing along his robotic cat Doraemon. Sewashi reveals that if Nobita keeps up his act, he will have a disastrous future: he will marry Gian’s sister Jaiko, have his private company burned down, and will be left with a great debt. To circumvent this, he orders Doraemon to help Nobita, modifying Doraemon’s nose to prevent him from returning to the future unless Nobita gains a better future.
Being reluctant until the threat, Doraemon introduces his gadgets to help Nobita which helps him immensely. Though Doraemon warns Nobita not to be too dependent on his gadgets, Nobita asks Doraemon to help him woo his crush Shizuka “Sue” Minamoto whom Doraemon reveals is the one Nobita will marry if his future is corrected. However, all his efforts end up making Shizuka become closer to ace student, Hidetoshi Dekisugi. Nobita’s attempt to be equal with Dekisugi by studying harder is futile, and he decides to let go of Shizuka to make her happier. He does this by flipping Shizuka’s skirt to reveal her underwear (but not looking at it), resulting in Shizuka slapping him and running away in tears. After a while, Shizuka starts worrying about Nobita. She overhears Gian and Suneo’s conversation about Nobita’s self-esteem getting crushed by Sensei for recently failing another test, causing her to believe he is planning to commit suicide, Shizuka arrives at the Nobi residence and resists Nobita’s people-repelling potion to help him, which Doraemon reveals is the first step in Nobita and Shizuka’s growing relationship to eventually becoming a couple.
After seeing his older self rejecting Shizuka’s invitation to a mountain climbing, Nobita disguises himself as his older self to help Shizuka, who becomes separated from her group during a heavy blizzard. His efforts to help Shizuka do more harm to himself, but this makes Shizuka feel that she has to accompany Nobita, saying “Yes” before collapsing from cold she contracted from her earlier conversation with Nobita. Forcing himself to remember the moment, the two are rescued by Nobita’s older self, who recalled the memory. Nobita learns from his older self that Shizuka was answering to latter’s proposition to marry her. It means that Shizuka will indeed marry Nobita. After hearing that Shizuka’s father has also accepted Nobita as his daughter’s spouse, Nobita and Doraemon return to the present timeline. Nobita visits Shizuka declaring that he will make her happy whatever it takes.
As Nobita’s future has been changed for the better, Doraemon’s programming commands him to return to the future in 48 hours. Noticing that Doraemon has a hard time leaving due to his worry for Nobita, Nobita confronts and has a brutal fight with Gian to prove that he is able to defend himself without Doraemon. Seeing that Nobita refuses to give up, Gian forfeits as Doraemon tearfully takes Nobita home before leaving in peace the next day. During April Fools, Nobita is tricked by Gian into believing that Doraemon has returned. In anger, he drinks a solution Doraemon gave to him which the opposite of everything the consumer says comes true. Finishing his retribution against Suneo (who was chased by a dog trying to bite him) and Gian (who was being dragged away by his mother who was preparing to punish him), Nobita goes back home while lamenting that Doraemon will never return. To his surprise, Doraemon suddenly returns and tells Nobita that he has gotten permission to stay with him because Nobita said that Doraemon would never return, still with the effects of the potion, and it became a truth. They both hug and cry in happiness.