Mephistopheles wa Dare?  

Who's Mephistopheles?, Who Is Mephistopheles?, メフィストフェレスは誰?

The night before Nanako's wedding, she discovers that her fiancé has been unfaithful. In the midst of this emotional turmoil, she encounters her priest who advises her to seek revenge against her husband for his betrayal. However, after meeting with a messenger from God who is two-faced and deceitful, Nanako must now decide whether or not to follow through with her plans for vengeance.