Alicia is a Master in the lunar Holy Grail War depicted in Fate/Extra Last Encore, serving as the guardian of the third layer of the Moon Cell automaton. Her true nature is that of an electronic ghost, a spirit without a living body. Originating from Britain during World War II, she was a young girl who was fatally wounded in an air raid. Although she was dying, the discovery of her magic circuits led to her being subjected to experiments that extended her life, only for her to eventually die in agony. However, her consciousness survived as data, wandering the digital network until she eventually reached the Moon Cell and formed a contract with her Servant, Caster.

Alicia takes the physical form of a small, eight-year-old girl with a deep fondness for the stories of Alice in Wonderland and Through the Looking-Glass. Her personality is childlike and defined by a profound sense of loneliness. Having spent an eternity playing alone in the digital space, she does not truly comprehend the brutal nature of the Holy Grail War, viewing it not as a survival competition but as an extended game of play. She dislikes doctors and the military, remnants of the trauma from her human experimentation, and her greatest desire is simply to have a friend to play with. She lacks any real will to fight or kill, and as a magus, her own survivability is remarkably low, even though her capacity to generate and control magical energy is immense.

In the story, Alicia is the master of the third stratum. Long before the events of the main narrative, she encountered the protagonist, Hakuno Kishinami, during a previous iteration of the war. The two became friends, and Hakuno promised to return to her after ascending to the next level. True to her desire for play over conflict, she allowed him to pass without a fight. After his departure, she waited for this promise to be fulfilled. To maintain her own fading existence over a millennium, she began absorbing the data of the "Nameless Forest," which caused her to gradually lose her human form and transform into a monstrous, mindless entity that continually rewound time on her layer, endlessly replaying the day she expected Hakuno to return.

Her key relationship is with the protagonist, Hakuno Kishinami, for whom she waits for countless years. She also shares a symbiotic and identical appearance with her Servant, Nursery Rhyme. In fact, Nursery Rhyme's very form as a Servant is shaped by Alicia's mind, manifesting through the Noble Phantasm "Nursery of the Stars" to create a reality mirroring her inner world. Another significant relationship is with her summoned monster, the Jabberwock, which she uses to create the "Nameless Forest" that ensnares intruders on her layer.

Alicia's development in the narrative is a tragic one. She begins as a lonely but gentle ghost seeking companionship. Over the course of her long wait, her desperation to survive and fulfill her promise corrupts her. She becomes a monster, not out of malice, but out of a broken, mechanical persistence to recreate the past. Her arc concludes when the protagonist returns, not as the friend she remembers, but carrying the book that was once her Servant. Seeing this, she finally abandons her endless time loop, regains a moment of clarity, and accepts her end, bidding farewell to him and wishing him well as he proceeds to the future she can no longer share.

Her notable abilities are derived from her status as a powerful electronic ghost. She possesses vast magical energy reserves that allow her Servant, Caster, to deploy and maintain large-scale reality marbles. The most prominent of these is the "Permanent Prison: Girl's Empire," a Noble Phantasm that allows her to rewind the state of her entire battlefield, effectively resetting an encounter to a previous point until a desired outcome is achieved. She also maintains the "Nameless Forest," a bounded field that robs intruders of their memories and sense of self, and can summon the formidable monster, the Jabberwock, to attack her foes.