In 2004 Nobita Nobi is a fourth grader who constantly gets failing grades in his subjects due to his laziness and is always bullied by his classmates Suneo Honekawa and Takeshi Goda. His great-great grandson from the 22nd century (year 2136), 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 becoming 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. Mistaking him 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.

Upon seeing his older self rejecting Shizuka's invitation to a mountain climbing, Nobita disguises himself as his older self to help Shizuka whom he thinks is separated from her group during a heavy blizzard. His efforts to help Shizuka do more hurt 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 the latter's proposition to marry her which means that the two will indeed marry. After hearing that Shizuka's father has also accepted her daughter's spouse, Nobita and Doraemon return to the present timeline.

As Nobita's future has changed for the better, Doraemon's programming commands him to return to the future in 48 hours. Noticing that Doraemon has a hard time to leave due to his worry for Nobita, Nobita confronts and have 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 turns all lies into truth and vice versa. Finishing his retribution against Suneo and Gian, Nobita goes back home while lamenting that Doraemon will never return. To his surprise, Doraemon suddenly returns because Nobita said that Doraemon would never return, still with the effects of the potion, and it became a lie. The two hug and cry in happiness.

https://en.wikipedia.org/wiki/Stand_by_Me_Doraemon
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