Doraemon Specials (1970) : 3x6

In the future, the mechanical robber Denja raids a bank and, after being captured and taken to hospital, uses a substitution trick to steal Doraemon’s body while the real Doraemon is trapped in Denja’s damaged chassis. Denja slips into the past posing as Doraemon and awkwardly ingratiates himself with Nobita and the other kids, even joining a baseball game to maintain his cover, while the real Doraemon scrambles to reach Nobita and reclaim his body. Chaos erupts when the authorities realize the escape, a frantic chase and several clashes follow, and Doraemon—powered by friendship and a repaired Time Belt—finally confronts Denja. Nobita recognizes the real Doraemon despite the disguise, Denja is exposed, apologizes, and returns the substitution rope; the police decide on rehabilitation rather than total destruction. The episode ends warmly with Doraemon’s identity restored, Denja moved by Nobita’s kindness, and a small birthday celebration that highlights friendship and forgiveness.