Mashu Kyrielight

Mashu Kyrielight is a Demi-Servant human fused with the Heroic Spirit Galahad. She herself initially does not know the identity of the Servant fused with her. In the year 2000, Mash was created from artificial fertilization and genetic editing. She is actually a Designer Baby, a magus genetically engineered under the orders of Chaldea's late director, ‎Marisbury Animusphere, to be a prime vessel for a Heroic Spirit's soul. The project aimed to control the powers of Heroic Spirits by binding them to a compatible mortal vessel in order to produce Demi-Servants.

In 2010, when Mash was aged 10, Chaldea performed their second Heroic Spirit summoning. While the project succeeded in summoning and binding a spirit to Mash, the spirit failed to awaken. Galahad decried Chaldea's brutal experiments, briefly taking over her body in an attempt to escape, but when Mash began to resist his control he realized that she would die in his absence. He remained in her body so she could survive, but refused to awaken. He would not form a Demi-Servant contract with her until the events at Singularity F, and even then he immediately returned to a dormant state without revealing his True Name to Mash after bestowing his abilities to her.

After the research team deemed the project a failure, Mash was left to Chaldea's care. However, due to being a genetically engineered organism not dissimilar to a Homunculus, her life-span was set since her conception. She was given eighteen years to live and while she was aware of this fact, she kept it a secret between herself and Dr. Romani, her physician. By the start of the story, Mash has already lived sixteen years of her life giving her a mere two years left, at best.