The Leo Blade (also known as the Blade of Moonstones), is a magical weapon crafted for Quentin Coldwater (to be used later on Martin Chatwin that is powerful enough to "tear through the fabric of magic itself".
The blade was originally created to be used by Quentin Coldwater (and then later Alice Quinn to kill The Beast, but it was stolen by Julia Wicker who used it as leverage to make a deal with the Beast to help her kill Reynard the Fox.
The blade was first discovered in Martin Chatwin's book at the Library, which described the blade as being able to slay almost anything, and that it hadn't been recovered by Martin after having been made. It is later shown that Quentin and Julia, after having traveled back in time over 70 years, have the blade commissioned by a blacksmith that a young Martin takes them to.
When Julia, Marina and Martin finally confront Reynard with the knife, they are interrupted by Penny, who runs into Julia and Martin, and teleports them to Fillory, causing the knife to fall to the floor. We then see Marina and Reynard both reach for the knife. When Julia returns to Marina's apartment, Marina is shown dead on the floor while Reynard and the blade were nowhere to be seen. It is currently unknown exactly what happened to the Leo Blade.
The blade also exists in the 23rd timeline and has been used to kill the The Beast of that timeline.
The blade can only be touched by Master Magicians. Its high concentration of magical power burns anyone who is not powerful enough to wield it. It has been stated that the blade is powerful enough to kill any magical creature, even a deity. This has yet to be proven, but it was capable of killing Martin Chatwin who was quite close to being on part with some of the most powerful magicians anywhere and even lesser gods.
- The creator of the Leo Blade also made the Virgo Blade.
- The blade takes approximately 70 years to make, due to the special properties of the moonstones.