About Ope Ope no Mi
The Ope Ope no Mi is a Paramecia-type Devil Fruit that grants the power to create a spherical domain, inside of which the user can freely rearrange, take apart (without harm), and "surgically" remodel anything and anyone, including themself, making the user a Free Modification Human (改造自在人間, Kaizō Jizai Ningen?, English: "Modification Man"). The fruit was eaten by Trafalgar D. Water Law, having been force-fed to him by Donquixote Rosinante. At some point in the past, the fruit's powers were held by a certain famous doctor.
The Ope Ope no Mi's power was first seen during the Sabaody Archipelago Arc, but the fruit was not named or explained in any way until the Punk Hazard Arc.
The Ope Ope no Mi is famed and coveted for letting the ability user perform miraculous surgeries, cure untreatable illnesses, and circumvent physical disabilities. It is also called the "Ultimate Devil Fruit" (究極の悪魔の実, Kyūkyoku no Akuma no Mi?) for its capacity to grant another person eternal youth in exchange for the ability user's own life, which is why the Marines were willing to pay as much as 5,000,000,000 to buy the fruit from a pirate named Diez Barrels over a decade ago.