Doraemon: Nobita to Mugen Sankenshi

Tired of the daily life and being the weakest, slowest, and dumbest, Nobita seeks comfort in his dreams where, using Doraemon's tools, he sets out on a fantasy journey. But when Nobita's dream world gets threatened by an evil sorcerer, Nobita gathers his friends to join him in his dream to fight the evil as the Three Musketeers.
(Source: Anime News Network)