This episode highlights why Luffy became so adamant about having a musician on his crew later in life—a direct result of his early admiration for Uta’s singing. Recommended Watching Order
"A Pledge for the New Genesis! Luffy and Uta!" One Piece Film: Red Episodio 1
Set approximately 12 years before the main story starts, before Luffy receives his signature eye scar or the straw hat from Shanks. This episode highlights why Luffy became so adamant
For the full backstory before watching the movie, viewers should watch the two specific tie-in episodes available on platforms like Crunchyroll : One Piece Film: Red Episodio 1