The Righteous Sun of the Pirates

An era of sweeping change, a steady stream of formidable fighters, mysterious Devil Fruits, powerful martial arts and swordsmanship, and the three forms of Haki... This sea swallows the remains of the weak and makes legends of the strong.

Charlie comes from another world. With swordsmanship as his foundation and a Devil Fruit power like a natural disaster, he also possesses all three forms of Haki. Armed with the justice in his heart, he vows to become a blazing sun in the sky and set this absurd world right.

(P.S. The protagonist starts out in the Marines, then joins the revolutionaries midway through. He starts with the Flame-Flame Fruit, which gradually evolves later on.)