Classic & Dark:
* Hellsing Ultimate (OVA Series): A brutal and stylish vampire series that follows a secret organization fighting against a growing vampire threat. It's violent, intense, and packed with action.
* Vampire Hunter D (OVA): This classic follows a dhampir (half-human, half-vampire) who hunts vampires. It has a strong sense of mystery and a unique art style.
* Trinity Blood: In a world where vampires and humans coexist, a priest becomes embroiled in a conspiracy with a powerful vampire. It's dark, action-packed, and explores themes of faith and power.
Mystery & Intrigue:
* Dance in the Vampire Bund: A mysterious vampire queen aims to create a society where humans and vampires live together. It's full of intrigue, political maneuvering, and a touch of romance.
* Blood Lad: A vampire king becomes fascinated with the human world and decides to bring a human girl to his world. It's funny, lighthearted, and has a compelling mystery element.
* Shiki: A quiet village is plagued by a series of mysterious deaths, and suspicion falls on a new family that has moved in. This is a psychological thriller with a strong sense of dread.
If you're looking for specific themes, here's a breakdown:
* Action-heavy: "Hellsing Ultimate," "Trinity Blood," and "Vampire Hunter D" are all action-packed and feature strong vampire characters.
* Mystery & Conspiracy: "Shiki," "Dance in the Vampire Bund," and "Trinity Blood" all have compelling mysteries at the heart of their stories.
* Light-hearted & Funny: "Blood Lad" offers a more comedic approach to the vampire genre, with a unique premise and quirky characters.
Remember that "Nightwalker" is a more obscure series, so finding something that perfectly captures its exact tone might be tricky. But the suggestions above should give you a good starting point for exploring the world of vampire mystery anime!