Since her parents passed away, Princess Mona lives by herself in a castle with two hideous, ghastly characters, Goomi and His Lordship. One day her sobs draw the attention of a unicorn, called U, who wants to comfort and protect Mona for as long as she needs. U becomes Mona's companion, her confidant and her inseparable friend. While Mona grows into a beautiful princess, a group of charming, peaceful and fanciful Yeah-Yeah’s settles in the neighboring forest. They have no particular special powers, yet they soon bring about major changes in everyone's lives, especially in Kulka, the dreamy musician.

Since her parents passed away, Princess Mona lives by herself in a castle with two hideous, ghastly characters, Goomi and His Lordship. One day her sobs draw the attention of a unicorn, called U, who wants to comfort and protect Mona for as long as she needs. U becomes Mona's companion, her confidant and her inseparable friend. While Mona grows into a beautiful princess, a group of charming, peaceful and fanciful Yeah-Yeah’s settles in the neighboring forest. They have no particular special powers, yet they soon bring about major changes in everyone's lives, especially in Kulka, the dreamy musician.