This paper model is the Winner's Proof, a Keychain for Sora's Keyblade that appears in Kingdom Hearts II Final Mix, which is a Japan-exclusive reissue of the Kingdom Hearts II video game, the papercraft is created by Mickey103.
Sora is rewarded with the Winner's Proof after satisfying the first twelve of the Mushroom XIII and returning to the Great Maw to find the thirteenth.
Winner's Proof displays exactly thirteen Mushrooms; four in the links and Keychain, two in the handle and the remaining seven on the blade, with one serving as the Keyblade's teeth. The Roman numeral XIII is shown just above the hilt and signifies the thirteen tasks you need to complete to acquire it. The head of the Keyblade forms a heart, bearing resemblance to the Ultima Weapon.
Winner's Proof's name comes from the fact that you have to pass thirteen tests, one for each Mushroom, to acquire it. [Source: khwiki]
You can download this papercraft model template here: Kingdom Hearts II Final Mix - Winner's Proof Keyblade Free Papercraft Download