Context: Monkey D. "Straw Hat" Luffy (Japanese: モンキー ・ D ・ ルフィ, Hepburn: Monkī Dī Rufi) is a fictional character and the main protagonist of the One Piece manga series, created by Eiichiro Oda. Luffy made his debut in One Piece chapter # 1 as a young boy who acquires the properties of rubber after inadvertently eating the supernatural Gum-Gum fruit.

Question: how did monkey d luffy get his powers?
Steam of consciousness below:

The relevant sentence in the passage is: Luffy made his debut in One Piece chapter # 1 as a young boy who acquires the properties of rubber after inadvertently eating the supernatural Gum-Gum fruit.
So, the answer is inadvertently eating the supernatural Gum - Gum fruit.