About Bari Bari no Mi
The Bari Bari no Mi is a Paramecia-type Devil Fruit that allows the user to generate barriers, making them a Barrier Human (バリア人間, Baria Ningen?, VIZ: "Barrier-Man"). It was eaten by Kurozumi Semimaru, and upon its reincarnation it was eaten by Bartolomeo.
The fruit's bestowed power is to conjure physical barriers out of thin air—either invisible or visibly transparent, resembling tinted panes or domes of glass; this is often achieved by the user making a finger-crossing gesture, though this does not appear to be required. Such barriers can shield the user against attacks, usually from the front, but also from other (or even all) directions depending on a barrier's given shape and position.
The barriers boast immense defensive power. Bartolomeo has a high opinion of his barriers' strength, as he was confident that they were "unbreakable" and could stop Doflamingo's Birdcage (which can slice stone buildings and enormous meteorites with great ease). Powerful attacks that the Bari Bari no Mi's barriers were able to completely block without the slightest crack include: