Echoes is a Mobian fennec fox who fused with Abyss Dusklight in ancient times, which was done in order to save her from death. They were sealed away in a crystal and transported to the modern day, where she met Skip Dawnstar-DeLune and his friends. You can probably tell from their shared, hyphenated last name how that went. Echoes is not certain about the nature of their home or why they were sealed away, but it seems to be a touchy subject.
Echoes's source was 15, but in the system, she is the same age as the body; in the intervening years between the events of their source and them being introjected, it seems that she adjusted quite well to modern life and technology with the help of her partner. Since joining the system, Echoes and Skip have formed a throuple with Ralsei, gotten married, and had a daughter.