from the derpibooru description:
My Little Pony, made even girlier… Somehow.

In the land of Endometria, Princess Menarchia rules, bringing a monthly flow to every girl in the land. One day she sends her prized pupil, Overnight Protection, to Periodville to learn about menstruation. Little do they know, the evil Crimson Tide, Princess Menarchia’s Sister, has been released from her thousand-year prison and will cast Menarchia into eternal menopause if not stopped.

Tune in to find out the heartwarming coming-of-age stories of Overnight Protection and her friends!

:D