Mahou Senshi Sweet Knights: Heroine Ryoujoku Shirei

Facing overwhelming demon forces, the magical kingdom of Roa and its elite Sweet Knights stand as the last line of resistance in a war their queen, Gloria, is losing. That premise sounds like standard magical girl territory — and on the surface, it plays that way. There's a hidden identity, an enemy infiltrating the human world disguised as a transfer student, and a heroine named Ririko Nanase who may or may not be connected to the Knights. The early setup has a genuine espionage angle to it: the villain Heinkel Metzer is methodical and patient, working covert intelligence before making any moves. It's more calculated than the genre usually bothers to be. This is a 2-episode OVA from 2004, adapted from a visual novel by Triangle, so the story moves quickly and doesn't overstay its welcome. The fantasy-meets-modern-world setting gives it a dual-layer feel — magical conflict running underneath an otherwise ordinary high school backdrop. If you've watched Mahou Shoujo Ai or Taimanin Asagi and liked the dark magical girl framing, this fits comfortably in that space. Fans of Bible Black who appreciate when a villain actually has a strategic brain rather than just raw power will find Metzer more interesting than the average antagonist. It's a hentai OVA, so go in with that understanding, but the narrative framing does more work than most entries in the genre bother to attempt.