Chiron

Chiron, also known as 2060 Chiron, is an asteroid in the Solar System, located between Saturn and Uranus in a group of planetoids known as the Centaurs. In part due to its irregular orbit, it has also been classified as a comet under the designation 95P/Chiron. Chiron was mentioned in the anime episode 14.

Chiron and Rui Saionji
Chiron was the celestial body controlling the energy of the young tennis player Rui Saionji. Nephrite used this knowledge to predict a peak in her energy, and planned to exploit and ultimately steal her life energy with the help of the Youma Tesuni, who was implanted into Rui's racquet.