The eldest son of the Ayanok�ji family and a genius, who was involved in the experiments to create Absolute Angels alongside his grandfather. Ky�shir� believes that he sacrificed himself in an attempt to quell the great catastrophe of ten years prior to the main time line of the story. S�jir�, however, has stated that for all his positive traits, Kazuya was a fool. Mika has added to this that Kazuya was as ruthless as a demon behind his eternal smile and tendency to always be victorious in any challenge. Ky�shir� looks up to him and makes every effort to emulate him, something his brother S�jir� has advised him against and which arouses Mika's hatred for him. Kazuya resembles the prince from Kū's dreams even more strongly than Ky�shir� does; her dreams of the prince are in fact memories of the time she spent in the lab, being developed by Kazuya and the other scientists.