Koutetsu no Majo Annerose

In Amidahara, a city so far gone that humans, demons, and criminals share the streets without much distinction, Annerose Vajra runs a detective agency. She's a half-demon witch who carries a legendary sword and has a reputation that keeps most people from bothering her. When a man named Rikurou stumbles into her world, moments away from being sold into slavery; she binds him to her service through a spell, making him her undead servant. Her other servant, Mitico, is not thrilled about the new arrangement. Then a girl shows up looking for her missing brother, and suddenly Annerose's detective work pulls the whole group toward something much larger and more dangerous than a simple missing persons case. The city has layers, and none of them are clean. If you've seen Taimanin Asagi and appreciated how it builds a gritty urban fantasy world with actual stakes, this hits a similar note. Fans of Bible Black will also recognize that dark supernatural atmosphere where the setting itself feels threatening. It's a 4-episode OVA, so it moves quickly: there's no padding here. The character dynamics between Annerose, Rikurou, and Mitico give it more texture than you'd expect, and the detective-agency framing keeps the plot grounded even when things get strange. Worth knowing upfront: this is a hentai adaptation of a visual novel, so it carries that territory with it. Go in knowing what it is and you'll get a surprisingly layered dark fantasy experience.