Secret of the Princess

Secret of the Princess (お姫様のひみつ, "Ohime-sama no Himitsu") is a yuri manga by Milk Morinaga. It is complete in one volume. Seven Seas has licensed it for English release.

Plot
Fujiwara is the school’s most admired student and captain of the volleyball team, but her reputation is at risk when she accidentally breaks the principal’s most prized possession, a priceless vase. Fellow student Miu witnesses the accident, and Fujiwara begs her not to tell. In exchange, she’ll do whatever Miu wants. It turns out that what Miu wants is to date Fujimaru! Although this wasn’t an arrangement that either girl expected, the two soon discover that breaking the vase may have been destiny’s way of bringing them together. (Official Synopsis)

Official
Official English site