This is as much as I remember: this one dude runs into a little girl that he has met before but has no memory of it and he turns into a werewolf. H also remembers that he comes from a lineage of werewolves that swore to protect the vampires, so the dude protects the girl from then on. That's literally all I remember. The little girl looked similar to the girl in the DOA franchise: Marie Rose. Please help.
Dance in the Vampire Bund is a manga about the vampire princess Mina Tepes and her protector Akira. Vampires have been in hiding for many years, but Mina wants to end their solitude and bring them out into the world of humans. She gets permission to create a special district for vampires only, called "The Bund" in Japan. In order to get this permission she pays off the entire national debt of Japan. She then reveals the existence of vampires to the rest of the world, and expresses her desire for the two races to live together.
Akira is the werewolf. Mina is the vampire.
Akira is the son of Wolfgang Regendorf, the head of the werewolf earth clan that is protecting the royal vampire family, the Tepes. He was raised from birth to be a strong fighter and devout servant of vampire queen Mina Tepes. He first met Mina a little after he was born, just as she got done with a purity inquiry. He then met her as a little boy at the age of ten. He found her in a garden crying and asked her if she was crying because she had a stomach-ache. That day, Akira promises to forever stay by Mina's side to protect her and keep her happy.
The first episode:.
Found by searching for anime werewolf protects vampire girl.