Himitsu no Himegimi Uwasa no Ouji  

Yurayura Fushigi Rikigaku, Wobbling Mysterious Mechanics, ひみつの姫君 うわさの王子

Roochen and Galnia have been at odds with each other for many years. With the recent establishment of peace between them, Princess Aldina from Roochen has been arranged to marry the Prince of Galnia. However, there are rumors that suggest the Prince of Galnia is quite promiscuous and spends most of his time engaging in reckless behavior. Aldina wants to verify these rumors for herself, so she decided to disguise herself as a boy and attempt to meet the prince privately.