Demonion: Gaiden

Sealed underground for two centuries, Astaroth — once powerful enough to drag the world into war before a band of heroes finally put him down — is back, and word spreads fast. Adventurers start flooding into his labyrinth, chasing fame and the bragging rights that come with slaying a legend. What they don't account for is that Astaroth has had two hundred years underground to think about what comes next. This 2-episode OVA is adapted from a dark fantasy visual novel, and it carries that DNA throughout — the labyrinth setting feels genuinely layered, full of traps and power dynamics that make every encounter feel loaded. Characters like Miska and Oboro aren't just window dressing; they're caught up in something that has real weight to it. The tone leans dark and deliberately paced rather than action-spectacle, so if you go in expecting that, it lands better. It's a hentai title, so that's the context going in — but if you've enjoyed the demon lord premise done with actual world-building in things like How Not to Summon a Demon Lord or Demon King Daimao, and you want something that commits harder to the darker end of that fantasy, this scratches a specific itch. Don't expect a full arc in two episodes; think of it more as a tone piece that establishes a world worth sitting in for a while.