The Nui Nui no Mi is a Paramecia-type Devil Fruit that grants the user the ability to stitch things together and un-stitch them like nothing happened. It was eaten by Leo.
Nui (縫,Nui?) means "to sew" or "to stitch" in Japanese.
In the Viz Manga and FUNimation subs, it is called the Stitch-Stitch Power.
Strengths and Weaknesses
This fruit allows the user to stitch objects to flat surfaces. It is very useful in pinning people to the ground as demonstrated when Leo was able to restrain Robin. The user is also able to undo the stitches to the object, as seen when Leo undid the stitches on Robin. In the anime, other dwarves were also seen undoing the stitches. However, the stitches do not harm its victim and do not appear to physically puncture the object. The stitches are strong enough to hold Robin down, and Leo was able to stitch Marine battleships together to prevent them from pursuing the Straw Hats. The ability can also be used on steel, implying that the hardness of an object does not hinder the sewing process.
This fruit does not have any known specific weakness besides the general Devil Fruit weaknesses. However, it seems that a sewing needle is needed for the ability to actually work.
Leo basically uses this power to stitch and hold down his targets. He also uses this ability to support objects, during earthquakes, to make sure they do not fall. It can also be used to reattach severed limbs, although irregular wound edges may compromise its efficiency and it will not heal the wound.
Haute Couture: Patchwork (高級仕立（オートクチュール） パッチ★ワーク,Ōto Kuchūru: Pacchi Wāku?, literally meaning "High Class Sewing: Patchwork"): Leo stitches several objects or persons to his opponent. Then, by pulling the thread with his superhuman strength, he causes all stitched objects to converge towards his opponent, crashing into them with great force. It was first seen used against Jora, stitching all of her comrades and subordinates around her.Haute Couture is French for "High Sewing" and refers to the practice of creating custom-fitted clothing.
As with the Mato Mato no Mi (which was referred to as the "Mato Mato Curse"), this fruit was not actually named in the manga. Leo referred to his "magic" as the "Nui Nui" power ("ぬいぬい"の力,Nui Nui no Chikara?), notably in hiragana rather than the katakana used in all Devil Fruit names. It was finally named and confirmed to be a Paramecia-type Devil Fruit in the One Piece Magazine.