Before Eidolon became the God of Fear, he used to be a human who lived in an era where people's faith in the gods were declining. He was the 4th out of 12 sons of a prominent noble family who are staunch anti-theists. An awkward shut in, he spends all day painting, much to the disappointment of his father.
Meanwhile, the disturbance caused by the great shift in the decline of faith caused the slumbering God of Fear, Phaino, to awake. With the decline of faith, his age and the "corruption" spreading across the spiritual realm, the god senses his inevitable demise and sought someone to help him to regain power in this time of scarcity.
Since the greater a celestials power is, the harder it will be to cross over into the mortal realm, Phaino needed an avatar, a vessel, in order to move freely and act on the spreading corruption. He approached Eidolon, whose timid and anxious personality suited his plans, by possessing a canvas and conversing with him. He promised the human various gifts and in return, to simply paint him a portrait, to give him form.
Eidolon, insecure and desperate for his father to acknowledge him, accepted. While he worked in the painting, he was bestowed with various abilities. The most significant of them was the ability to see the future. With this ability, Eidolon was able to assist his father in his conquests and they eventually managed to rule a massive empire.
This made Eidolon extremely grateful for the god and enthusiastically worked more on the painting. Some of his brothers did notice his odd behavior and how he is losing sleep and appetite just to work on it. He has also became protective of the painting and would shut down any concerns his brothers would have about him, worsening the already aloof relationship he had with them. Yami, the youngest and only brother he is close with, also started getting worried about Eidolon's obsession with the painting but he just told him every time to not worry.
Eventually, time passed and the painting neared it's completion. Phaino smiled as Eidolon put the finishing touches and with the last stroke of the brush, he felt the barriers start to break and he burst out of the painting and into the mortal world. The sheer power released upon the god's summoning wounded Eidolon, causing the man to lose his eyes.
It was Yami who discovered him on his room later, lying bloody on the floor in front of an empty torn canvas. The young man panicked and immediately called for the healers.
The next day, Eidolon's father found out what he did. He was enraged that his son summoned a "devil" and his recent contributions were from dealings with it. Despite his other sons and the servants' protests, he burst into the infirmary carrying his sword, intending to strike Eidolon with it. Yami tried to shield his wounded brother but he was easily pushed to the side. However, before his father's sword was able to reach him, Phaino whisked Eidolon away to his realm. He genuinely came to like Eidolon, and as the man is now basically exiled from his own family, the god offered to make him a part of his own instead by marrying him to his only remaining daughter, Mirissa.
And so, Eidolon remained in the Phaino's realm. As he could no longer paint due to the loss of his eyes, he shifted his skills into music (which was previously only a minor hobby) and in no time was able to master the strings. It was said that his voice was so gentle and captivating it could comfort even the most disturbed of souls. It weren't long before the cautious and hostile Mara, the Phaino's fae, became enchanted with him. Phaino, who knew that he would not last long due to the corruption, became relieved that he can leave his realm in capable hands. He formally assigned Eidolon as his successor and upon his death, he bestowed upon him a final gift: his core, an orb containing all of the God of Fear's power. And so, Eidolon became the new God of Fear and remains so up to this day.
