Along with Saber we have two other characters Joan Of arc Saber and unknown for Fate/Grand Order Typemoon new smart phone game. Fate /stay night co-creator Kinoko Nasu talked about the unnamed female in an interview with 4gamer.
“She’ll be the heroine this time around Just like how Saber is the face of stay night and Joan is for Apocrypha, [the new heroine] is the face of Fate/Grand Order. Saber and Joan will be key characters, but more in the role of famous Heroic Spirits. The one who will be the main character is the girl holding the shield.”
Interesting enough the unknown woman was suppose to appear in original Fate/Stay Night anime but it didn’t work that way. The article goes to explain that once players get their servants they will find out who they are. This is the opposite of the series as servants identities at least the main are a secrete from the masters and in some cases the servant. With that in mind the creators are asking those who get the game to please not spoil anything for other fans.
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