Saiyuki Requiem(2001)

Gensou Maden Saiyuuki: Requiem - Erabarezaru Mono e no Chinkonka

The gang is traveling along when they find a girl in need. Of course, they all can't resist going after her. This girl isn't all that she seems... her motive or her "humanity".... and soon the whole gang has Sanzo's past on their hands and one certain young boy who can keep a grudge for decades...

(Source: Anime News Network)