Tsubasa Kawai is a fifth-grade student in class 5-2 and one of Ryōta Satō's close friends. He possesses a calm and kind personality, frequently displaying an innocent smile. Within their friend group, he often mediates conflicts between Ryōta and Kōji Imai, showcasing his diplomatic skills. Academically intelligent, Tsubasa holds a strong interest in astronomy, pursuing this passion through reading about outer space and regular stargazing activities.

His physical appearance differs between adaptations: in the TV series version, he has blond hair, while in the OVA version, his hair is depicted as black. His assigned number on the class list is 8.

No concrete information exists regarding Tsubasa Kawai's background story, character development, or expanded role across other official media such as movies or spin-offs. His portrayal remains consistent as a supporting character focused on maintaining harmony among peers and pursuing academic interests.