The Guilty Thorn was a short spear, made entirely of a single black metal. The entire blade was about a metre in length, with an approximately thirty centimetre-long grip, a long handle, and a sharp fifteen centimetre point at the end. The main feature of the spear was the rows of short, sharp barbs that ran along the entire length of the handle, making it difficult to remove the weapon from its target without a high Strength stat and mental strength.
In the anime, the spear was dark red with silver edges and a small piece of tattered red fabric tied to a hole at the end of the grip.
In 2024, Caynz and Yolko requested Grimlock to create some piercing weapons with damage over time effects for their plan to determine Griselda's murderer. Thus, on April 19, Grimlock created three such weapons, including the Guilty Thorn.
On April 22, at 18:27, Caynz stabbed himself with the Guilty Thorn outside the town of Marten on the 57th Floor, then teleported into a church within the town via a Corridor Crystal and waited for the durability of his armour to decrease sufficiently, before hanging himself from the window of the second floor. The moment his armour was about to break, he used a Teleport Crystal to disappear, making it seem he had been killed within the Area.
Later that day, the spear was taken by Asuna and Kirito to be appraised by Agil, who determined the weapon's name and maker. Later that night, the Guilty Thorn was taken from Kirito by Schmitt when the former arrived in Lindarth. The next day, on April 23, after Yolko faked her own death within the Area, an unsettled Schmitt returned the short spear to Kirito.