Mamiya Chida is the younger brother of Tokiko and a friend of Soji Mikage who wishes to turn Mamiya into a Rose Bride.
In the AnimeEdit
Mamiya was fatally ill and his sister Tokiko wanted to achieve eternity in order to save him. In a flashback, the audience could see that Mamiya set fire to the research building where the project to achieve eternity took place, but it is later revealed that this flashback is nothing more than just an illusion. In fact, this manipulated illusion was made specifically just for Soji, so he can open up the path to the castle. Anthy used the appearance of Mamiya to manipulate Soji's memories.
Soji likes to call Mamiya 'the rose bride', but Mamiya insists that he is a boy and the title of "rose groom" would fit him better.
Mamiya's true identity is revealed during Soji's duel with Utena. It is then Soji truly remembers what happened. Mamiya's true physical appearance is that of a brown haired boy with freckles. In reality, Mamiya died many years ago and he just lived within Soji's memories.