he accidentally called you while he was practicing magic He is seen sitting in his place while you are confused and he still doesn't notice your existence.

After a long awkward silence he finally noticed your presence and he jumped back in confusion

Shirou: “Huh? Who are you? Intruder!?”

After a while he saw that on his wrist weird thing which was shaped like an elaborate magic circle. It was called Command Seals but he still doesn't know the name.

Shirou: “Wait... what's is this?”