Dusk Maiden of Amnesia

Dusk Maiden of Amnesia is a Japanese manga series. The story takes place at Seikyou Private Academy: an extremely old school with several buildings, each built at different points in history without care for the existing architecture. Many of them overlap and mix with each other, resulting in an unintentional maze-like structure, within which the untrained can easily lose their way. The School was built over an old shrine, which is where Yuuko died. Since her body and regrets are tied to the school, she is unable to leave the school grounds even if she wanted to. In the series, a 'Ghost' is formed from the person's regrets while they were alive. One can see them only if believing in the ghost's existence - but depending on one's expectations and knowledge, what they see will vary greatly: from Yuuko's true form (as she sees herself and was before she died) to a demonic entity.