Not sure if something like this has been mentioned before or not, but I've always thought it was an interesting idea, so. . .
Name: Block-Block Fruit (a pun because it "blocks" attacks and the areas are in various geometrical block shapes such as cubes, rectangles and squares)
Type: Paramecia
Description: Allows the user to create nearly invisible (there is a slight outline of the edges and corners) three dimensional blocks of various sizes that protect anything inside or behind them from enemy attacks. Can be used to surround the user and others to protect them, placed in midair to allow the user to stand or walk on (giving the illusion of flying, though technically the user is just walking on a solid object) or trapping an enemy inside of them. Also possesses the ability to shrink blocks as well as any inanimate object inside of them into 1x1inch cubes that can be stored and "reopened", retrieving the objects from the cubes and restoring them back to their normal size. This allows the user to carry indefinite amounts of items of varying sizes with them when it would otherwise be impossible.
Weaknesses: Lacks any real offensive ability forcing the user to rely on other combat skills. The larger the block, the more difficult it is to maintain and create. Barrier blocks can be broken if the opponent is significantly more powerful by continually attacking the block, forcing the user to focus on layering blocks and eventually tiring him out to the point that he can't continue creating block layers. Shrinking and storing aspects do not apply to living/animate beings or objects. Standard DF weakness apply as well, of course.