Mamiya Chida is the younger brother of Tokiko Chida and a close friend of Souji Mikage. He is a mysterious, androgynous boy who suffers from a terminal illness, a condition that quietly torments him and makes his time limited. He is drawn to the scent of roses and tends to the flowers in his sister’s garden, finding comfort in them. Mamiya’s motivations are rooted in his illness and his bond with Mikage: Mikage wishes to turn Mamiya into a Rose Bride, a role Mamiya resists by insisting that “rose groom” would be more appropriate for a boy. In the story, Mamiya serves as the emotional catalyst for the Black Rose arc. Mikage believes that by killing Anthy Himemiya and making Mamiya the Rose Bride, he can use the power of eternity to cure Mamiya’s fatal condition. Mamiya’s presence drives Mikage’s actions and the creation of the Black Rose Duelists. Mamiya has a notable ability: he selects the targets who become Black Rose Duelists by offering them a rose that grows in an aquarium. Initially, the rose matches the color of the targeted Student Council member, but as the target is decided, the rose gradually turns black, indicating the selection is complete. However, a crucial twist reveals that the Mamiya who appears throughout most of the series is not the real Mamiya Chida but Anthy Himemiya in disguise, acting under the guidance of her brother Akio Ohtori to manipulate Mikage. The real Mamiya had already died from his illness, and it is suggested that Mikage himself may have set fire to Nemuro Memorial Hall, either as a sacrifice to save Mamiya or because Mamiya was already dead. Mamiya’s voice is heard in Mikage’s final duel, hinting at his lingering influence. His key relationships are with Mikage, whom he addresses as “senpai” and who is devoted to saving him, and with his sister Tokiko, who also sought the power of eternity to help him. Mamiya’s development is limited by his early death, but his role exposes the themes of sacrifice, manipulation, and the desperate search for immortality that permeate the Black Rose arc.