Anaklusmos

Riptide, or in Anaklusmos in Greek, is a magical sword used by Percy Jackson.

The sword is extremely powerful, and just like other weapons and items it is disguised as a modern day object, in this case a ballpoint pen. When it is "uncapped", the pen extends into a sword. Percy can never lose this magical tool due to its magical ability to always reappear in his pocket in its pen form. The sword was given to Percy by Chiron, who got it from Poseidon before the events of The Lightning Thief.

Anaklusmos is made out of Celestial Bronze, and because of this it cannot harm mortals, only immortals, monsters, and other demi-gods due to its properties. This is made evident in The Lightning Thief when Percy is affronted by a gang of humans and yet again in The Titan's Curse when Percy accidentally attacks Rachel Elizabeth Dare. Anaklusmos has been used to kill many monsters, including the Furies in The Lightning Thief. It is humorous to note that Percy was at first disappointed by the gift, as it took the form of the ballpoint pen at that time.

History
Anaklusmos is a great source of help to Percy, and saves his life many times. It also has a long and tragic history. It originally belonged to Zoë Nightshade, a former Hesperid and the fifth daughter of Atlas, the Titan General. Zoë had used this sword, which at that time took the form of a pin rather than a pen, to help Hercules to escape the dragon Ladon and to seize the Golden Apple. As a result, Zoë was banished and exiled for helping a hero. Hercules has also betrayed her later on and thus she had since forsworn men and joined the Hunters of Artemis.

When she first saw Percy with the sword, she was disgusted. However, on her deathbed, she told Percy that he was no Hercules and she was happy to see him with the blade .

Name
The name Anaklusmos is Greek for literally 'wash against' (ana=against, klyzein=wash). But it is referred to as Riptide in the books, even though its official title is Anaklusmos. The name was revealed immediately after Percy had received it from Chiron. This is a fitting name for the sword as Percy Jackson is the son of the sea god Poseidon.