Index is one of the main heroines and the titular character of the series. She is a young nun from Necessarius, a branch of the Church of England. Index is small in stature and has a petite build. About 12 or 13 years old, she has thigh-length, silvery-blue hair with very white skin and large green eyes. She also wears a white robe with golden embroidery sewed onto every edge of it, the Walking Church, that prevents any injury on her, but it is later destroyed by Toma when he touched it with his right hand, which is why her uniform is stitched with golden pins.