S0E56 · Doraemon's Long Day (2009)

On Doraemon’s birthday, Nobita plans a surprise celebration, but the two end up in a huge argument after the dorayaki are ruined. Doraemon angrily returns to the future with Dorami for a medical checkup, but while at the hospital he accidentally swaps bodies with a dangerous fugitive robot named Denja. Taking advantage of Doraemon’s appearance, Denja escapes and heads toward Nobita in the 21st century, while the real Doraemon, trapped in Denja’s body, desperately tries to return home and warn everyone before it’s too late.