Yo-Jin-Bo: Unmei no Freude

Sayori is a history enthusiast and member of her school's history club. On a club excavation she finds a jade pendant buried in the mud and brings it home. That night the pendant begins to glow green and establishes contact between Sayori and a ghost: Hatsuhime, a princess who lived in the castle the club has been digging up. From this point on Sayori has access to a world and a story she was not expecting to be part of.