The Ope Ope no Mi is a Paramecia-type Devil Fruit whose ability is to create a spherical domain in which the user can freely rearrange, take apart (without harm), and generally remodel the structure/anatomy of anything and anyone (themself included) in a “surgical” way, making the user a Free Modification Human.
The Op-Op Fruit is known and sought-after for enabling the user to carry out miraculous operations, treat incurable illnesses, and even get over physical limitations. It is also known as the “Ultimate Devil Fruit” because of its extraordinary capacity to bestow eternal youth upon a recipient in exchange for the user’s own life.
I’m not sure if anyone has thought about this yet. But pretty much all operations Trafalgar Law performs, he also has the ability to undo. He can cut people and things, and then put them back together. Shambles, Room, Takt, Mes can all be reversed. So why would the Perennial Youth Operation be the only one that can not be reversed?
My theory is that Law poses the biggest threat to Imu as he is potentially the only one who can reverse Imu’s theorized immortality. This might be why this fruit had such a big bounty of 5 billion berries, which is higher than any of the recent emperors. Only bounties higher than this were Roger and Whitebeard.
My guess is that similar to the original Operation, the user has to sacrifice themselves. For example, assuming it is a procedure with steps A-B-C to grant immortality, you’d do C-B-A to reverse it. The cost would be the same, user’s life.
There are theories that Law might be inclined to perform the Perennial Youth Operation on Luffy, but Luffy isn’t the type of person who would want that. So it makes more sense that Law will save Luffy at a juncture where Luffy might be in mortal danger from Imu.
I envision him throwing a truth bomb that any Operation can be reversed by a skilled enough doctor, even the Perennial Youth Operation. Then proceeds to undo Imu’s immortality and sacrifices himself in the process, proclaiming that his D comrades will bring another storm/dawn! Instead of making Luffy immortal, Law will cancel Imu’s immortality, so they can have a fair fight.
Theory by noobChurn (https://www.reddit.com/user/noobChurn)
