One Piece: I Lie Flat from the Start and Become Invincible by Sunbathing

Su Yang transmigrates to the world of One Piece and gets a System that makes him stronger just by basking in the sun.

The day he was tied to a pillar and left to die, Luffy passed by and hauled him aboard.

From then on, the Straw Hat crew had a strange new member. While everyone else fought, he sunbathed. While they went on adventures, he sunbathed. Whenever the ship docked, he found a high spot and kept sunbathing.

The day of the Summit War, the sun was blazing, and he spent the whole day basking in it.