Kyouya cared a lot about his sister Utai, as he always guided her gently but firmly. He also stood up for her when she wanted to continue performing Noh.
Kyouya was the second child born into a family of Noh performers. Much like other children born into Noh families, he had started performing as a kokata – a child actor in Noh theater – from a very young age. Unlike the majority of such children, however, he intended to continue down the path of performing and become a Noh performer.
When Utai learned that she could not become a Noh performer, he gave her Brain Burst to distract her from Noh, but it instead made her fall deeper into its spell, until a year later, he pleaded with their grandfather to allow her to continue to perform. Their grandfather insisted that this could not be done, and Kyouya was shoved by his elder brother, which caused a large mirror to fall onto him, which killed him.
Kyouya's duel avatar is a rare two-colored avatar, being both silver and white. His silver half is metal, while his other half is that of a regular avatar. Shinomiya Utai has said that she had not seen anyone else with a half-metal color.
It has been theorized that two-colored avatars come from having two separate, distinct identities within oneself from before they became a Burst Linker.
Mirror Masker's Child is Ardor Maiden, his younger sister.
- Theoretical Mirror – This ability gives Mirror Masker absolute defence against all light-based attacks. Any light based attack on him will be broken into numerous smaller light rays and dissipated.
- Shinomiya Kyouya (四埜宮 竟也, Shinomiya Kyōya)
- Mirror Masker (ミラー・マスカー, Mirā Masukā)
- Theoretical Mirror (理論鏡面（セオレティカル・ミラー）, Riron Kyōmen (Seoretikaru Mirā))
- He was born 4 years earlier than Utai.
- He is the first character in the franchise to be the Parent of their younger sister and die at a young age, the second being Chigira Souya, and the second of three older brothers of female Burst Linkers to have some tragedy befall him, after Kusakabe Rinta, the third being Souya.