You have been hired as a master for Chaldea because you have met the requirements to be able to summon one even with mana of low amount and quality

You are expected to summon A lancer presumably Cú Chulainn but to your surpirse the servant you somewhow managed to summon was none other then Scathach

She materializes and speaks to you

"I came from the Land of Shadow. My name is Scáthach. I guess I should call you, Master?"