Hilda Dietrich (ヒルダ･ディートリッヒ Hiruda Dītorihhi) is a teenage girl who lives on the island of Growerth with her brother Michael Dietrich and her parents. She spent her childhood with the siblings Relic and Ferret von Waldstein, mingling more with the Night than the Day.
In 2005, her heart is carved out by Juna Riebeluka. She is saved from death thanks to Dimguil Sunford, who had bitten her on her ankle prior to the incident. He turns her and makes her a vampire so that she does not die.
Her new life is not without problems: once in a while, Hilda's heart is subjugated again, throwing her into a "death-like state." Relic cannot even turn her into a flock of bats with his own powers without a mysterious power blocking his efforts.
Relic and Hilda decide to head to Japan to find the mysterious Kumanobe Clan on the Doctor's advice, since the doctor has heard that the Kumanobe Clan holds some clue to changing turned vampires back into humans.
Hilda dislikes humanity because humans tend to fear and hate and kill vampires for no reason. It drives her mad.