Ion is a Medusan who offers Zero a physical body on Ovidia IV, a gift that comes with hidden dangers.
Ion is a Medusan, a member of Zero's noncorporeal species. In Is There in Beauty No Truth?, Zero makes contact with Ion, who offers to give them a new physical body, and Gwyn persuades Dal to detour to the planet Ovidia IV so that Zero can accept.
On Ovidia IV, noncorporeal beings create bodies able to touch, smell and taste, and Zero joins the Feast of Senses. Dal and Gwyn learn that such bodies degenerate away from the planet and that Zero faces a deadly ritual, the Running of the Nazamon, before Zero chooses to leave.