The Gravity Blade (重力剣, Jūryokuken) is a magic sword owned by Touta Konoe.
30 years ago prior to the story, UQ Holder's trial cave was the hideout of a certain wizard. This wizard made a magic sword and left it there. The sword was said to be difficult to wield so it had been abandoned and stuck in the cave for years. It was later pulled out and taken by Touta. It is a black katana.
This sword is a blade with the ability to increase its "gravity", or, more accurately, weight. Doing this increases the relative power of the blade's physical strikes on an opponent. Located on the hilt of the blade, under the guard, is a dial which has a "heavy" and "light" setting, flipping the dial in either direction allows Touta, or any other user, to alter the blade's weight, heavier for increased power, lighter for ease of use. At 200x of its original weight, Touta makes a comment that it feels like a body builder, at 50000x of its original weight, simply throwing the blade is enough to completely destroy a small palace with ease, as demonstrated by Jinbei Shishido. The sword was in fact created and owned by Albireo Imma. After Touta leaves UQ Holder Headquarters its revealed that the gravity blade is able to talk to Touta when both are alone, and that it was originally created to help those connected to "3-A". While little of its personality has been explored, the Gravity Blade shares a similar personality to its implied creator, Albireo Imma.