It is the curse of the devil fruit. When they eat the fruit they gain new power and new skills but the cost of this new power means they must lose something like the ability to swim. They have not explained exactly why this happens.
Luffy or Monkey D. Luffy was able to stretch because of the devil fruit (Akuma no Mi) he ate which was the Rubber Rubber Fruit (Gomu Gomu no Mi )
The Mera Mera no Mi was offered as a prize at the Corrida Coliseum. The event was won by Sabo who took the fruit and ate it, inheriting Ace's former powers.
He ate the Gomu-Gomu Devil Fruit, which had been found by the Shanks pirates.
Luffy - Gomu Gomu no mi - Rubber rubber fruit, Tony Tony Chopper - Hito Hito no mi - Human human fruit, Nico Robin - Hane Hane no mi - Bloom bloom fruit, Brook - Yomi Yomi no mi - Rebirth fruit.
Luffy can't swim. Devil Fruit users gain superhuman powers, but at the cost of (in a world that is over 90% water) being unable to swim. Seawater drains their energy, and makes them helpless. Some can resist partial immersion, but they are basically useless in water, they are nicknamed 'hammers'.
Luffy or Monkey D. Luffy was able to stretch because of the devil fruit (Akuma no Mi) he ate which was the Rubber Rubber Fruit (Gomu Gomu no Mi )
The Mera Mera no Mi was offered as a prize at the Corrida Coliseum. The event was won by Sabo who took the fruit and ate it, inheriting Ace's former powers.
Monkey D. Luffy was seven years old when he consumed the Gum-Gum Fruit, also known as the Gomu Gomu no Mi.
of course there are no stories.....
He ate the Gomu-Gomu Devil Fruit, which had been found by the Shanks pirates.
durian
Gomu Gomu Fruit, or the Rubber Fruit
The powers are unique to the user, and are not inherited from one's parents. Big Mom has dozens of children, none of whom share her devil fruit powers, and many of whom have devil fruit powers of their own.
Luffy's crew are the main heros in One Piece, there for they are most likely not going to die. One of the crew, Brook, has died once before but was brought back to life by the powers of his Devil Fruit.
I'm not sure, he's a rubber man so he cannot be lost in a match.. but if someone had the small gum gum fruit as his . POSSIBLY NOT ## So I asked a lot they said no and no at the last episode he not going to die.Paradise Heaven™
The fruit that he eats is the "gumgum fruit"
Luffy - Gomu Gomu no mi - Rubber rubber fruit, Tony Tony Chopper - Hito Hito no mi - Human human fruit, Nico Robin - Hane Hane no mi - Bloom bloom fruit, Brook - Yomi Yomi no mi - Rebirth fruit.