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 timeline, Nobita experienced nothing but misery and misfortune throughout his life. As a result of this, Nobita's failures in school and subsequently, his career, have left 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.
Doraemon has a pocket from which he produces many gadgets, medicines, and tools from the future. The pocket is called yojigen-pocket, or fourth-dimensional pocket. Some of the gadgets are based on real Japanese household devices with fanciful twists, but most are completely science fiction (although some may be based on folklore or religious stories). Thousands of dōgu have been featured in Doraemon. The number of dōgu has been approximated at 4,500. It is this constant variety which makes Doraemon popular even among adult readers/viewers. In the series, the availability of dogu depends sometimes on the money Doraemon has available, and he often says some dogu are expensive in the future. The more famous ones include the "bamboo copter", a small head accessory that allows flight; the "Anywhere Door", a door that opens up to any place the user wishes; and the "Time Machine".