Solo is the only prince of the Seed Kingdom hence his name. (But a little brother was born to them in these days.)

In the hollow Mysterious Planet, seven kingdoms co-exist, all of them lit by the Sun's Blessing from the Kingdom of the Sun, in the middle of the planet. The light of the core sun is necessary for the continued existence of all the kingdoms. Yet, something is causing the Sun's Blessing to weaken. If something isn't done, it will be the end of life in the Mysterious Planet. Fortunately, the twin princesses of the Sun Kingdom, Fine and Rein, have been endowed with the magic of the Prominence, and are looking for a way to fix things. <br><br>
(Source: Anime News Network) 

Fine and Rein are sent to the Royal Wonder Academy on the Royal Wonder Planet in order to study to become better princesses. They plan to make many friends, but unfortunately, the competition and cold nature of the students and teachers make things impossible. The twins also become Universal Princesses when touching the legendary Soleil Bell, releasing two angels named Pyupyu and Kyukyu to help aid them. Unfortunately, an evil force manifested in a painting doesn't seem to be satisfied about the Universal Princesses... <br><br>
(Source: Anime News Network)