Father Simon was the local priest of Alimango Island. He was the one who taught Shirley to read and write due to a lack of a school on the island. After Norikata Emiya and Kiritsugu Emiya arrived on the island, he became vary wary of Norikata for the following year.
Simon normally shows a gentle disposition, but harshly judges Norikata Emiya as a heretic. He warns Shirley being around him will cause her to be "ensnared by the devil."
Simon is shown speaking to Shirley, urging her not to return to Norikata's home for work. He instructs Shirley to carry a silver knife with her as a warding talisman. After Shirley drinks the potion that turns her into a Dead Apostle, Kiritsugu goes to Simon for help. They find the remains of the chickens she preyed upon, but she is nowhere to be found. Simon contacts people off the island for help, leading to the Holy Church and Mage's Association to exterminate the island, and goes to warn the villagers. Simon is turned into a ghoul while warning the villagers, later killed by Natalia Kaminski while he is about to attack Kiritsugu.
Father Simon is only briefly mentioned in the original novel, lacking any lines. He is given slightly more attention in the anime adaptation.
 Fate/Zero material - Encyclopedia: Shirley [Person's name], p.097
Shirley [Person's name]
A native of Alimango Island, where Emiya Norikata chose to sequester himself away from the outside world. Though the educational environment she grew up in was extremely poor – she did not even attend elementary school, and only learned reading and writing from the local priest – it was enough to stimulate her ample intellectual curiosity, and by the time she was 13 years old she had already received a master's degree through correspondence courses alone. Of course, this talent did not go unnoticed by Emiya Norikata. He brought her on as his assistant, putting her in charge of handling all the miscellaneous daily tasks in the Emiya household.
While she did receive some training from Norikata, it was not at the level of being taken on as his disciple. He simply taught her the basics of the basics, and nothing more. And really, even calling it that much is a stretch. All he actually did was interact with her without bothering to hide his true nature as a magus. Nevertheless, Shirley's innate thirst for knowledge allowed her to absorb Norikata's words at an astonishing pace, and he expected great things from her in the future. However, as the old saying goes, "Curiosity killed the cat." In the end, her inquisitive mind brought about a tragedy.
She was the young Kiritsugu's very first love. It seems that the reason he ended up pampering the kendo girl he met in his later years so much was because she reminded him so much of Shirley.