Riptide

Riptide (in Greek, Anaklusmos) is a magical sword, currently in the possession of Percy Jackson, that is made out of celestial bronze, a material that is only effective on magical creatures. When used on mortals, the sword passes through them as if nonexistent. Mortals also do not see Riptide as a sword, but as a sort of modern gun.

One of Riptide's most interesting features is the fact that it takes the form of a ballpoint pen (that reads "Anaklusmos" on the side) when not in use. Once the pen is uncapped, it transforms into its functional sword form. It is almost impossible to lose, as it is enchanted to appear in Percy's pocket if it is somehow lost. However, if Percy doesn't have pockets the pen doesn't return.

Given to Percy by Chiron in The Lightning Thief, Riptide was formerly owned and used by the demigod, Hercules. The sword originated as Zoë Nightshade's hairclip, which she gave to Hercules to help him defeat the monster Ladon and is said to have the ocean as its source of power, which would explain why it works well for Percy. Hurcules did not give Zoë any credit for killing Ladon, leaving her to her to face the wrath of her father and sisters alone. this betrayal was the basis for her later hatred of male demigods.

Percy has a dream in The Titan's Curse that shows Zoë giving her hairclip, which turns into Riptide, to Hercules. Chiron tells Percy the sword has a tragic history, which includes Hercules leaving Zoë to the wrath of her family.

Use
Used in close combat, and is light and balanced in wearers hands. Riptide can destroy monsters, since it is made out of celestial bronze. But cannot hurt or kill mortals, as "they aren't important enough". When accidentally or even intently swung at mortals, the blade simply passes through them.

In the books Riptide is summoned when you uncapp it but in the movie you have to click it.