Tsubasa Yuiki is the younger brother of Yaya Yuiki. After he was born, Yaya became jealous of all the attention her parents gave to him, so Pepe was born from her desire to stay like a baby and get all the attention.
Yaya tricked the Guardians into her house so that they would baby-sit Tsubasa for her. At the end it was Amu who told her how blessed she should feel because she has a little brother, as she retold to Yaya her initial feelings after Ami was born. Amu's feelings were more like frustation and dislike rather than jealousy because her parents wanted to rely on her help to look after the house and sister. Despite all that, Amu told Yaya that a big turn around of those feelings for her infant sister was when Ami's first words were 'big sister' ("oneesan"), intead of saying "papa" or "mama" which are the most commoly first words a baby says. From that moment on, as Amu told Yaya, she began to care for Ami more sincerely and lovingly. Though Amu didn't say exactly 'lovingly', the tone of her voice,she truly cared for Ami.
Tsubasa has light orange/brown hair and light skin, and he normally has his eyes closed, but when he has them open, his eyes are brown like his hair. Unfortunately for Yaya, Amu and the other Guardians all thought that Tsubasa was very cute. It appears that he is about a few months to 1 year old.
- Yaya Yuiki - Tsubasa's older sister.
- Nodoka Yuiki - Tsubasa's mother.
- Daisuke Yuiki - Tsubasa's father.