One Piece

Soul of the Demon - The next time you hit a creature with a melee weapon attack, your weapon flares with white-hot intensity, and deals an extra 1d10 fire damage to the target and causes the target to ignite in flames. At the start of each of its turns, the target must make a Constitution saving throw. On a failed save, it takes 1d6 fire damage. On a successful save, they extinguish.