Doraemon Movie: Boku, Momotarou no Nanna no Sa

Doraemon is sent back in time by Nobita Nobi's great-great grandson Sewashi to improve Nobita's circumstances so that his descendants may enjoy a better future. In the original time-line, Nobita experienced nothing but misery and misfortune manifested in the form of poor marks and grades, physical disasters, and bullying throughout his life. This culminates in the burning down of a future business he set up which leaves his family line beset with financial problems. In order to alter history and better the Nobi family's fortunes, Sewashi sent him a robot called Doraemon.