In centuries passed, there existed a group of Priests and Paladins that aggressively fought against the threat of the ancient Occultists. This group, known as the Luminai, was blamed for torturing cabals of Occultists and destroying their historical texts in a period known as the Burning Times. One of the most prominent members of the Luminai was Dawn, a priestess.
Dawn was imprisoned by Countess Belladona after a failed attempt on the vampiress' life. Gladius, the only other remaining member of the Luminai, ventured to Belladona's Keep to rescue her and was also forced into her service. It wasn't until the War of the Divine Child that Gladius and Dawn were able to escape. They came into possession of the Eye of Proteus and began the process of cleansing the Chaotic Taint from the realm. When the ritual failed, Dawn's life was taken.
When Sarapis saw the selfless courage and devotion that Dawn demonstrated in this act, He granted her the gift of immortality. From that point on, she would be known as Mithraea, Goddess of the Sun.