@OnePiss
It wasn't mentioned much, but the baby Luffy in Uta-chan's drawing? I wonder if it was his mother who was nursing the baby Luffy in Uta-chan's drawing.
Maybe Luffy's love of singing was influenced by his mother....
I don't think they put that much setting in the manga for the movie characters, but it would be interesting if it was foreshadowed that way.
It would also be interesting to see how far Oda-sensei, whose synonym for adventure is mother, would go in portraying Luffy's birth.