Moon Observatory is a fantasy otome game series created by Batensan.

In the universe of MO, there are thirteen worlds named after months, with one final nameless world. Each world has a Magician, a half-immortal being who watches over their world's residents.

This story centers on Melanie's task to apparently save the world, a role given to her by the mysterious Magician Ven. However, it seems as if he isn't telling her everything...

Melanie's "partner-in-crime" Shisui is the only one who seems to realize, but at the same time wants to preserve her innocence.

Melanie runs head-first into the world with accepting arms, while Shisui curses it for forcing a cruel fate on Melanie.