Properly written "Star Seed." Sailor Moon reference, specifically the Stars season (
year 5). A tiny, glowing crystal that represents the vital force and purity of its owner.
Galaxia (the main villainess) is after these for galactic domination, but ordinary Star Seeds have very little shine and quickly turn black when separated from their owners. Said owners then become "
Phage Senshi," who must be wounded critically and healed by Eternal
Sailor Moon's second-tier healing magic.
Active Star Seeds do not fade to black upon removal from their hosts, and are sources of great power. As far as we know, only a planet's Senshi possess these. It is possible to live without a Star Seed, if you are given strong enough magic (as in
Galaxia's bracelets). Active Star Seeds can apparently also take on different forms; Galaxia's Star Seed became a young girl who called herself ChibiChibi, for example.