William smiled, he was right she was smart using the momentum of Caster along with her weak hold on the sword to disarm her. 
"Using strength to knock away my sword, that is tied to my mana via blood, as is Caster." And the sword flew back to Williams hand.

"Can I use one of my noble Phantasms? Either he is very strong indeed, or my feminine charms are nullified by that infernal magic resistance" Caster asked. She didn't like this man, not at all. 

Caster raised her staff infused it with her mana gripping it tightly, "I guess this is harder than expected Caster, a Saber that has magic resistance vs a Caster than can't use their Noble phantasms. I guess I will just have to step up." William said grabbing Gram tightly and went to stand next to Caster, Gram started to glow with a light aura. And William charged in first with Caster behind him. Both Caster fueling him with enforcement magic and Gram giving him ancient magic William was known to hold his own against some servants, although he had lost his leg during the Berserker fight last year.