Ikuko Kamiyashiki is an actor affiliated with the theatrical troupe Sirius. Within the context of the story, she holds the position of a senior or前辈 to the protagonist, Kokona. Her primary function in the narrative is to help orient both new characters and the audience by explaining the specific circumstances and internal workings of Sirius to Kokona and her peers.

No reliable information is available regarding her personality, deeper personal motivations, specific role in the plot beyond exposition, key relationships with other characters outside of her status as a senior, character development over the course of the story, or any notable abilities she may possess as a performer.