Medusa

Medusa is a Rider Class Servant. She has unmatchable speed and her noble phantasm(s) are her chain spear daggers. She used to be the servant of Shinji Matou, but she couldn't stand him. She's now the servant of Sakura Matou, who she sees as her own daughter. Sakura is fragile and doesn't want to participate in the 5th Holy Grail War, so Medusa is protecting her. She's a cold blooded killer to anyone who wants to do harm to Sakura, but not Shirou Emiya, because he's Sakura's best friend.