Hell Knight Ingrid

As the Hell Knight for a supernatural organization called NOMAD, Ingrid hunts demons in a Tokyo quietly being eaten alive by demonic forces. She's hunting Sabato Kiryuu, a traitorous scientist who flipped sides and needs to be brought down before he causes serious damage. Sounds straightforward enough, until she tracks him to a church and the tables turn hard on her. That's basically where the series kicks off, and things get considerably darker from there. This is a 4-episode OVA from 2009, adapted from a visual novel in the same universe as Taimanin Asagi and Taimanin Murasaki, so if either of those did anything for you, Ingrid is basically a companion piece set in the same grimy supernatural world with familiar power systems and that same heavy atmosphere. The animation holds up reasonably well for its era, the character designs are detailed, and the soundtrack leans into the dread in a way that actually works. There's a betrayal-and-consequence thread running through the story that gives Ingrid's situation real weight beyond just the surface-level setup. It's a mature, intense watch — the hentai tag is accurate, so go in knowing that — but fans of dark supernatural settings with actual lore behind them, similar to what you'd find in Disgaea's tone of demons-and-politics worldbuilding, will find enough here to stay engaged. Short runtime, dense atmosphere, worth the time if the genre fits your taste.