Quote Originally Posted by Ryllharu
Archer spoke to Ilya as if he knew her. Most importantly, all his references to her were referring to the past. "You haven't changed...".
-This should tip you off that Archer has intimate knowledge of the people currently in the war, since Ilya was unknown to everyone but Rin (and her only through reputation). Past tense it what's really weird, since Ilya is quite young. That's odd enough, but once you know who he is you understand why.
That's actually the part that put me on the wrong track. For the longest time I thought Archer was from the past and that Ilya was a reincarnation of someone Archer once knew very well.