White Knight: King of Eos

14 year old prince Soichiro Kugo lost his home Eos when he was 4 to shinigami (Gods of death) and has been hiding since. One day in the year 759 on a hunt he encounters a shinigami and attempts to kill it but the shinigami reveals itself to be his late sensei Chozen Kaibaro. Chozen informs him that Soichiro has to find 15 regalia (Royal weapons) that once belonged to his ancestor's to gain a form called arminger which will help him stop the shinigami king and end his reign of terror.