In the manga, a Sailor Guardian who protects their respective planet possesses a special Star Seed called a Sailor Crystal. Star Seeds are the life force of individuals - they are the soul of a person. Star Seeds are born in the Galaxy Cauldron, but some of these Star Seeds develop into Sailor Crystals, which grow into planets and guardians for those planets.
Because each planet can have only one Sailor Crystal, each planet has only one Sailor Senshi. Sailor Crystals enable Sailor Senshi to transform and give them their powers. When Sailor Guardians die, they can be reborn as long as their Sailor Crystal exists. The Crystal returns to the Galaxy Cauldron to be reborn, so that Crystals are inside each Sailor Senshi at birth, with the exception of the Inner and Outer Sailor Guardians whose Sailor Crystals were given to them by their Sailor Power Guardians.
Sailor Crystals are not mentioned in the anime; It is only mentioned that Sailor Guardians have true Star Seeds which don't turn black when removed and continue to glow for all time.
List of known, Named Sailor Crystals
- Sailor Moon has the Silver Crystal.
- Sailor Mercury has the Mercury Crystal.
- Sailor Mars has the Mars Crystal.
- Sailor Jupiter has the Jupiter Crystal.
- Sailor Venus has the Venus Crystal.
- Sailor Pluto has the Pluto Crystal.
- Sailor Uranus has the Uranus Crystal.
- Sailor Neptune has the Neptune Crystal.
- Sailor Saturn has the Saturn Crystal.
- Sailor Chibi Moon has the Pink Moon Crystal.
- Prince Endymion has the Golden Crystal.
- Sailor Galaxia has the Sapphire Crystal.
- Guardian Cosmos has the Cosmos Crystal.
- Prince Endymion is the only known male character (and also the only non-Sailor Guardian) to possess a Sailor Crystal.
- According to Naoko Takeuchi's notes, the Sailor Starlights' Sailor Crystals were contained in their transformation brooches.
- Other than Sailor Moon and Sailor Chibi Moon, all of the other Solar System Sailor Guardians had heart-shaped crystals.