Around a week ago I finished a short manga titled,
Secret of the Princess by Morinaga Milk [お姫様のひみつ (Ohimesama no Himitsu)]. It's published from 2012 'til 2015 in 1 Volume (6 chapters + extra).
How is it possible for Miu to get in touch with her prince as a student in all-girls high school? Who's going to be her prince?