Sakura and Shirou
Sakura frowned in response to his question, unsure how to answer it.
"Erm, well, they're like ghosts", she said, really unsure how to explain it any better.
"To be more specific, they're ghosts of ancient heroes, summoned as magical familiars. I've never actually fought one myself, though. I have summoned one once, though, as did Senpai, but that was as part of a special ritual, we couldn't do it normally", she added, not failing to notice the slightly sad look on Shirou's face at the mention of the Grail War and the servant he had once fallen in love with.
Once, Sakura would have felt jealous at the look on his face, but not any more. She knew that, whilst Shirou had been and, in some ways, still was in love with Saber, he also loved her with all his heart, and even if Saber was to somehow return, he would never abandon her.