A sunstone was a piece of the moon that was affected after the Astral Gate accident. It was believed that spatial fluctuations were absorbed in the stones and, further, that the energy can be released and amplified by the Sun.
Pao Pu-Zi collected two sunstones. He left one on Mars for his daughter to find while he kept one to open a pocket in hyperspace in order to hide from the Blue Snake crime syndicate. Pao Meifa and Jet Black on the Bebop used Meifa's stone to open the pocket by having Spike Spiegel shoot it with his ship, the Swordfish II.[1]