A distant cousin to Eithan, he gave up his position as heir to the Blackflame branch of the Arelius family to Eithan so that he could marry Naru Jing.
Cassias follows a Path of sword madra, like Yerin.
His only technique shown is the Silver Step. It is an Enforcer technique with Striker elements developed for quick movement over a small area. His Goldsign is a silver bracer on his arm. He was ranked the second best Highgold after his wife Naru Jing. His ranking as a Truegold is not known.
Cassias is on the Path of Silver Grace. He studied under the prestigious School of Silver Grace to develop relations between them and the Arelius family.