Ginka Saginomiya

Ginka is Isumi's great-grandmother. She is 91 years old. She demonstrates a high capacity for fighting, as shown in volume 11, when she tries to defeat Hayate. However, this was all done because she was worried about her great granddaughter, whom she cares very much for. Ginka normally looks like a young child, but this is only because she is able to stay healthy and alive by sucking on other people's blood. Source Wikipedia