[ waver definitely notices the frantic tone in shirou's voice and takes a step back in reflex.

however, when he thinks about it...he hasn't met many masters at all. saber's master was einzbern... lancer's was his professor... and he saw the king of heroes in the tohsaka mansion so perhaps he was their servant?

but shirou just made a distinction between himself and the tohsakas, so that can't be it.

so that leaves...berserker, assassin or...caster? ]

I don't really know them by name... your last name's Emiya, right? That's what it said on the profile. If that's the case then I don't know. Which servant did he have?