Riptide

Riptide
Riptide is Percy's sword that is made out of celestial bronze that kills immortals only.(When Riptide is not in full form, it is a ballpoint pen) The blade will pass right through a mortal boy/girl. Riptide was given to Percy by Chiron. Riptide is mentioned in all the books in the series. Book 1 is when Chiron, disguised as Percy's latin teacher, gives him the weapon.