This papercraft is Dirk's Unbreakable Katana, from MS Paint Adventures webcomics, the paper model was created by aiko-chan14. The Unbreakable Katana was in the possession of Dave's Bro at the beginning of the comic.
Bro used it in the fight with Dave and Lil' Cal. He also used it to split the meteor that was supposed to strike Dave's apartment. He lost the sword when he fought Jack Noir in the Land of Heat and Clockwork. It stayed stuck in the Beat Mesa after the attack with Noir, much like the sword in the stone. Jack discovered that the sword had some strange golden energy flowing through it, perhaps from the cracked Beat Mesa, and decided to take it with him. He later returns it to Bro in what appears to be an attempt to finish their duel from before. Bro is then impaled by Jack with his own sword, after Jack gets prototyped a fourth time. Dave eventually comes upon Bro and his sword, and decides to try to, much to the dismay of Terezi. He fails and promptly makes a .
Post-scratch, this same sword can be found in the possession of Dirk Strider, nestled in Cal's arms. The Brobot seems to own one as well, which it used in its Strife with Jake. It is apparently very sharp, capable of cutting through drones, which are ostensibly made of metal. While the other post-scratch kids all alchemized better weapons for themselves once in the Medium, Dirk was shown to still use the original katana, perhaps indicating its reliability.
Given its relatively bland appearance, it is surprisingly one of the seven legendary weapons of cherubim folklore, and was originally forged by a Japanese master over the heat of a roaring manga fire and cooled in an enchanted spring where virgin horses bathe. Being that its appearance in the comic is based on an actual image, it is arguably this sword. Ironically, the sword it is based off of is very low priced and anything but unbreakable. [Source: wikia]
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