Michi Hate no Mukou no Hikari

A saint and a knight, and the story of their meeting and separation with a village girl. Yuna, a plain village girl, suddenly lost her plain day to day life. After being requested to by a mysterious light in a bright white world, Yuna finds herself in the body of a beautiful saint. However, what awaited her there was: the contemptuous gaze of the saint's fiance, First Holy Knight Asyut; the cold detachment from her attendants and the tense atmosphere of the entire palace. Yuna, alone in her crippling confusion, still tries to fulfill her duty as the saint's substitute, until one night when she discovers the saint's sins beyond the spiral staircase… (Source: yumemirusekai.wordpress.com)