A character from the Fate/stay night doujin series "Sword Dancers", by Himura Kiseki.
Not a genderswap of Archer, but a completely original character based on Archer.
A version of Illyasviel von Einzbern who has become a Counter Guardian with similar abilities to Archer. Himura drew this character on an end card for episode 6 of the first season of the Fate/kaleid liner PRISMA☆ILLYA anime adaptation.
Nobody here but us chickens!