Ayaka is the archetype version of Shirou Emiya who was to be the protagonist of the original Fate/stay night novel that was never finished. She would have an insecure personality and hold a negative view of herself. Unlike her older sister Manaka, who was regarded as a genius at magecraft, she would only have mediocre skills causing her to develop an inferiority complex towards her. She would come from a line of magi and be aware of the upcoming Holy Grail War and her expected participation in it, as opposed to Shirou who was orphaned and largely unaware of the world of magecraft. She would refuse to take part in the War however due of the deaths of both her father and sister in the previous War.

Much in the same was as Shirou, she would end up joining the War summoning Saber (a male archetype of Fate/stay night's Saber) to protect herself, just as Lancer was making the killing blow against her. At some point during the War she would catch the eye of Archer (himself an archetype of Gilgamesh) and be proposed to, causing him to view Saber as his rival. She would eventually lose Saber as her Servant to Sancraid Phahn, Master of Berserker. Lancer, who at this point would lose his Master to a curse on her, would form a contract with Ayaka to save Saber. She would also be poisoned, with Archer taunting Saber with the cure leading to a climatic fight between the two.

As the story was left incomplete to be rewritten as Fate/stay night, the fate of Lancer is unknown as well as what took place with her inevitable encounter with her now resurrected sister Manaka, 1st Master of the War and Master of the Beast.

While not to the obsessive degree of her sister, she views her Servant Saber as her Prince and ideal protector.

She has a cameo in Fate/school life as an ordinary student at Shirou's school.

(Source: Type-Moon Wikia)