Crux originaly was abit of a schizo but was cured when he met a girl named Sonaline when he was around 16 (current timeline he is 26). She taught him how to use his powers properly but she died when he was around 20, he shattered abit and he could no longer use his powers properly till Kain took him in for about 2 years.
Then he met Myo Kiyoshima and he was able to repair himself abit and use his demon sword DemonBrandt to its full potential and his Dark powers again in unison. Sometimes in the human world he visits her grave in memory of his former master.

This is just some background information on Crux Vessalius, brother to the Demon King Kain, former student to Sonaline the Dragon Princess, and fiancee to Myo Kiyoshima. Enjoy and if you have any questions ask me below.