The Modo Modo no Mi is a non-canon Paramecia-type Devil Fruit that grants the user the ability to generate pink energy which returns anyone and anything twelve years younger, which lets the user become a Return Return Human (モドモド人間 Modo Modo Ningen). It was eaten by Ain.
This fruit’s main strength is that it allows the user to turn back the age of anything and anyone they touch, precisely twelve years. This can not only weaken or incapacitate an opponent, but also attack enemies in creative ways: for example, by transforming igneous rock back into its original state, this causes lava to erupt from the ground and injure an opponent, while reverting the ground back into a solid state after the foe is wedged into it to entomb them. By touching a person enough times with this ability, it can effectively kill the target by reverting them to before they were born, erasing them from existence.
MAG.MOE - The MAG, The MOE.