In the manga, a guardian Senshi 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 senshi. Sailor Crystals enable senshi to transform, and give them their powers. When a Sailor Senshi dies 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 senshi at birth.
Sailor Crystals are not mentioned in the anime. It is only said in the anime that Senshi 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 as her Sailor Crystal.
- Sailor Mercury has the Mercury Crystal as her Sailor 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 as his Sailor Crystal in the manga and anime and the Rose Crystal in the video game "Sailor Moon: Another Story".
- Sailor Galaxia has the Sapphire Crystal.
- Guardian Cosmos has the Cosmos Crystal.
- Mamoru Chiba is the only known male character (and also the only non-Sailor Senshi) 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 Senshi had crystals shaped like hearts.