I'm just spitballin' here, but I think the silver knife might have been originally intended for Remilia. If the author believes the fanon rumor that Sakuya was originally a vampire hunter, Sakuya might have originally substituted silver knives for silver bullets, but retired them once she left the Vampire hunting business.
...Well, whatever. I'll need time to hone my ki, so we'll do it tonight at three.So, what were you planning to do with that one?I put the others away so I wouldn't stab any innocent maids.Please don't be late.You know what?I forgot.You too.