It was roughly seventeen years ago, back when the Second Titan War was well under way. About a year before the Battle of Manhattan, Theia, one of the elder prophetic Titans, foresaw the fall of her allies. She confided this to her husband and brother, Hyperion, and asked his opinion about it. The Titan of light feared for his future, and came up with a solution: mate with a mortal woman, in which the demigod born would be his vessel and the one to help him come back to power. Putting mind over matter, Theia agreed to his plan.
So Hyperion disguised himself as rich man, in hopes of finding the perfect woman to become the mother of his vessel. That was when he laid his eyes upon Priscilla Iglesias, a Spanish immigrant in Santa Fe, New Mexico. With little time left on hand, he did everything he can to earn the trust and love of Priscilla, and he didn't try in vain. Soon, their affair led to her pregnancy; in the process, Hyperion left a part of his essence to inhabit the body of the unborn child, which became his link to it, and his last resort, set aside reformation at Tartarus.
Several months later, Hyperion and Priscilla's child was born, and was named Agnes. Almost that exact time, the Titan, and the rest of Kronos' army, was defeated and sent to the depths of Tartarus once again. Agnes, on the other hand, lived a pretty normal life at Santa Fe. She gained loads of friends at the private school she attended, and became well-known throughout the city for her stunning beauty. In fact, her physical appearance was attributed to her Titan parentage, for she was literally "bright-looking". Unbeknownst to her, Hyperion's essence inside her developed at an alarming rate, and by the time her scent was enough to be followed by monsters, they were completely linked with each other.
Agnes was then thirteen years old, when Hyperion's voice began speaking to her. She thought she has gone insane, and tried dismissing him; however, the Titan was impatient already, for his reformation was taking way too slow. He kept speaking to her, and when she was attacked by a hellhound, he told her to fight it. Agnes' first monster fight had gone almost out of hand, and she blasted light everywhere, despite Hyperion's guidance. Ever since that encounter, she realized the truth of the voice's words, and promised that she would listen to him. Still with Hyperion's voice guiding her, Agnes trained every dead of night, fighting off monsters that caught her whiff. With every session she underwent, she became stronger and finely-attuned to her powers.
Soon, her father explained to her the true purpose of training her and all that whatnot. At the time, she became too proud of herself that she became blinded by his rewards, and so she followed suit. She secretly left home to Mt. Tamalpais, the stronghold of the Titans, under the guidance of her father. He sent one of his followers, a son of Krios, to accompany her, and their mission was simple: kill demigods in his name by reciting a special spell crafted by the Titan himself. The blood of these demigods hastened the rise of the Titan, and the duo killed enough to reform one-fifth of his body, which would have took a much later time.
The countless slaughters has turned Agnes into a bloodthirsty person, which became a way for Hyperion to possess her through his essence inside her. At one point, the possessed Agnes went on a frenzy, which led to the death of her partner, Priscilla, her friends and schoolmates, and innocent mortals. The cries and final breaths of those who trusted Agnes managed to reach deep inside the girl, and she broke free from the possession. In light of these events, she became enlightened to her father's manipulations, and renounced her sworn duty to him. She only realized this three years after, and she was sixteen by then.
She wandered throughout New Mexico with no apparent plan at all, until Apollo noticed her. She told him her story, and the god deemed her worthy of his pity. He took her under his wing, and made her one of his immortal servants on Olympus. However, Hyperion's voice still tried persuading her to come back to him some time after. It was too powerful that sometimes, his remnants inside Agnes overtook her, and she was basically possessed by the Titan. She went into violent outbursts and lost control of her powers, only to be sedated by the gods themselves.
On a trip to Camp Half-Blood, Agnes came across the Hunters of Artemis. She felt that she was safer in their company, because joining the Hunt meant losing her demigod powers. She asked him if she could be a Huntress. He complied to her request, seeing that she served him well, despite her condition. She took the oath, and became one of the hunters thereafter. Hyperion, on the other hand, wanted her back even more than before, and possession wasn't enough. He sent one of his followers yet again, this time a child of Lelantos, named as Cesar Matias, to bring her back to his service.
While on the hunt at the forests of Maine, Agnes asked Artemis permission to temporarily leave the hunt for Santa Fe. She wanted to check on what remained of her rampage about a year ago, and to at least pay respect to those she killed, including her mother. The goddess permitted her, yet the air of uneasiness clung. While she was at her home, now abandoned and decaying, she was knocked out by a gust of wind, sent by Cesar himself.
On the way, she tried getting away from him, because she highly suspected that he was sent by her father, but soon saw this opportunity to prove to Hyperion that she wasn't his pawn, that she wasn't running away anymore from him, and that her resolve was stronger than his coercions. After thinking about it carefully, she theorized that the only way to fully free herself from Hyperion was to kill herself, which meant killing the essence inside her. Yes, she cooperated with Cesar, all the while preparing herself for the sacrifice she was going to make, which would probably save the whole world from an impending destruction.
On their pit stop at Sleepy Hollow Cemetery, they were found by a group of camp demigods that were sent to retrieve Agnes. Cesar fought for her, but was defeated. She, on the other hand, was confused and distracted on what to do, and was easily subdued. On the way back to camp, Cesar escaped, but not before promising to her that he will come back for her. Now that she has arrived at camp, she decided to stay there for a while because she had caused enough trouble to the hunters.