"I am purchased [by your household]"
Oh, of course, she couldn't just be a maid or servant but an actual slave/indentured servant kemonomimi girl whose infatuated with him and is willing to risk her life for him in combat (y'know, MAID STUFF). Why not just skip beating around the bush and have her come out and say, "Master! Let me ride you like a pogo stick and we'll have enough babies to start a village together!".