Ore to Kanojo wa Shujuu na Kankei

After the main character's mother's funeral ceremony, a maid suddenly appears in front of him. According to her, his grandmother wants to talk to him. He immediately visits her house, and finds out that he is one and only heir. But, to inherit the property, he'll need to complete several missions. And three maids offer him to become his exclusive maids. With their help (including sexual ones), he completes the missions one by one. But, it's just a matter of time until he falls in love with them....