Ryuuhei is Kouhei's grandfather and a powerful spiritualist. Kouhei lives in his household, which is located in an antique shop. He agreed to take Hazuki in out of kindness, though he appears to have other motives for it as well including ascertaining the whereabouts of his daughter Shizuru (Kouhei's mother).

(Source: Wikipedia)

Morioka Kouhei wants to become a photographer. Unfortunately, he has the tendency to unintentionally capture the images of ghosts on film. 
One day, he visits an old castle in Germany where he meets a vampire girl, Hazuki. It turns out that Hazuki is confined in the castle against her will. She tries to turn Kouhei into her slave by sucking his blood, with the intent to have him break the device sealing her in the castle. Although Kouhei proves to be immune to the vampire's curse, he is eventually forced to help her. Hazuki successfully escapes from the castle and leaves for Japan to look for her mother. 
When she arrives in Japan, she goes to Kohei's house where he lives with his grandfather, who agrees to take in the girl. Due to his own childhood experiences, the sympathetic Kouhei agrees to aid Hazuki in her quest. 
However, other vampires, including Elfried and Count Kinkell, manage to track Hazuki to Japan. They will stop at nothing to retrieve her. 
(Source: AnimeNfo)

Mugihito is a Japanese actor, voice actor and narrator from Musashino, Tokyo. Mugihito was formerly credited under his birth name and also Mugihito Amachi (天地麦人).

Omake Special from the final DVD volume. The Special storyline has very little to do with the original series outside of having some of the same characters, and has a completely different storyline which does not fit into anything which came before it.

Ryuuhei Midou