Engraved Pleasure

About Engraved Pleasure

Robert, the prince of the Kingdom of Corinth, promised Arieno, the sole daughter of a farmer in his territory,
that he will enroll together with her in a military academy in two years.
However, soon after making the promise, Arieno goes missing.
Two years later, when Robert was about to head to the military academy, Arieno, who had become his servant, was waiting for him.
Why did Arieno suddenly go missing, and what happened during her two blank years?
Robert comes to know about this question through assignments at the military academy.