In the anime, One Piece Monkey D. Luffy is the main character.
His story starts when a group of pirates arrive at his village when he was just a child, the name of the group was the red-haired pirates.
Luffy becomes friends with them and even starts to idolize the leader, Shanks.
One day a different pirate crew put the anchor down. On that day, Shanks, his team, and Luffy were at a bar.
They get made fun of by some mountain bandits, but though shanks just laugh it off, Luffy becomes angry and eats a mysterious fruit at the counter table in his irritation. Shanks realizes it and immediately tells him to choke it out, but it’s too late. Luffy then gets informed that it was one of the legendary devil’s fruits, the gum-gum fruit, and now he became a rubber man, but he can’t swim anymore since a devil’s fruit user is weak towards the water and instantly starts to drown.
Though learning that he has powers, he goes to the bandits to get revenge but being a kid, he didn’t help that much and got easily caught.
Shanks and his pirate crew come to rescue him, but it’s too late. They already threw Luffy in the water and, worse, a sea monster was going to eat him. Shanks jumped after Luffy and snatched him just in time, but he lost his arm because of the creature.
When the time has finally come for the red-haired pirates to go, Luffy is still crying and declares that someday he will become the greatest pirate in the world and obtain One Piece, the hidden treasure of Gold. D. Roger, the now-dead pirate king.
Shanks gives his straw hat to Luffy and says that it is imperative to him and return it someday when he becomes a great pirate.