Kuroinu ～The proud saint is stained with white filth～

What happens when the war humanity is already losing gets betrayed from within? The central conflict of Eostia's medieval fantasy world, a century-long struggle between humans and dark elves, is genuinely interesting, right up until the mercenaries hired to fight it decide they'd rather conquer everyone themselves. The Black Dogs, led by the brutal general Volt, are supposed to be humanity's hired muscle against the dark elf queen Olga Discordia and her monster armies. Instead, they betray their employers, ally with orcs, and declare their own nation built on dominance and subjugation. The people who were supposed to be saved suddenly have new oppressors wearing familiar faces. Standing against all of this are seven princess knights, including the compassionate High Priestess Celestine Lucullus, who represent the last organized resistance against Volt's regime. The world-building here is genuinely detailed for what it is, there's real political history, faction dynamics, and a sense that this setting existed before the story started. If you've watched Taimanin Asagi or Bible Black and know what you're signing up for with this genre, Kuroinu is considered one of the more polished entries in that space, adapted from the visual novel by studio Majin across six OVA episodes. It's dark, it doesn't soften its edges, and the action framing around the betrayal arc gives it more narrative structure than most comparable titles. Go in knowing the tone and it delivers exactly what it promises.