Xunthas

Xunthas, a star from the constellation Ara that was brought to earth and tied to Cyaro by Gaia in order to protect Adrasteia.
Xunthas was introduced when the party decided to try and make contact with what seemed to be a sentient creature in the crystal structure that formed in Cyaro's arm. Xunthas seemed just as perplexed as to why they have been trapped in Cyaro's arm and so looks for their guidance on it. When Cyaro suggests that it is in order to protect Adrasteia. Xunthas doesn't really understand this task or mortals for that matter, soing things like making Adrasteia fall unconcious in order to keep her safe, though Cyaro managed to convince them to follow their way of doing things.
Xunthas proves to be a good protector even risking their life facing Quintus Pterygas after Adrasteia was taken, and getting heavily injured in the process. 
After some time a bond is created between Cyaro and Xunthas and they even bless one of Cyaro's books making it a holy book and prompting Cyaro to become a Twilight Cleric. However, this does not last as when Cyaro ends up accidentally teleporting to the Ashen Wastes and then accidentally calls upon Achlys to get herself out of the predicament getting trapped by the Mist Goddess in a dreamscape, Xunthas sacrifices themself to get them out.
The last that has been seen of Xunthas is Cyaro having a dream where they are being tortured with the remains of other stars by Achlys.