If you want to get your monster maids, you'll need to work for them.
One night, you see a shooting star. As a joke, you wish to have monster girls as your maids at your service. You don't expect it to actually work, but as soon as you look away, you see a bright light shine right into your face, almost as if something were running straight into you. Either way, you are transported into a black void. Then a translucent girl with light for hair appears before you. In your shocked state, your eyes go down to her massive breasts.
"Human, I have heard your wish. And to grant it, I will transport you to the world of monster girls. But to make them your maids, you will need to best them in a challenge, as per the world's rules."
"Oh, just like No Game No Life!" you point out.
"What- What's that?"
"Oh it's this anime where the world is defined by games and stuff instead of fighting."
"That's dumb. This world isn't like that. You can only get monster girls to become your maids through challenges. And those challenges can also include fighting, if the monster girl you challenge wants it. Now good bye" The translucent girl waves her hand and causes another flash of light to blind you.
You wake up in an empty field of grass. You look around and see not much except for...