flat eskardos
Master of Berserker (Fate/Strange Fake) and one of the students under tutor of Lord El-Melloi II. A talented magus with a personality that is best described as "carefree", "naive", and "good-hearted", he joined Snowfield Holy Grail War to befriend humans and servants alike.
His existence is actually part of Eskardos family's forgotten plan that is still going on for 1800 years, explaining the powerful magic circuits, and the purpose itself is "to bring the future to the past". It is unknown how much Flat knows about the plan, or if he knows about it in the first place...