Should the name of the main character in "Fate Kaleid Liner" be "Illya" or "Ilya"?
Both "Ilya" and "Illya" are official spellings of her nickname. "Ilya" is used on the TYPE-MOON's official website and in the fan translation of the game, but "Illya" tends to be used elsewhere, especially in merchandise. 


Illyasviel von Einzbern Wikia Page: Citation 3