Ruu is an alien baby from the Planet Otto, who can levitate and perform telekinesis on objects, and who develops a deep affection and love for Miyu and Kanata, likening them to his parents and often assisting and helping them. He uses his abilities at the most inappropriate times causing Miyu and Kanata great trouble. Although he is still only a baby, he can understand everyone perfectly. In order to keep the others from knowing the truth about Luu's identity, he is referred to as Miyu's little brother (although Luu will deny that and insist on calling Miyu "mama").

(Source: Wikipedia)