Ojou-sama wa Himekishi

One day, the main character is appointed as the chief butler of the Rain family. He doesn't take it seriously and just lives a busy life taking care of three daughters. He, however, needs to arouse the power of heroines asleep inside them as well. It seems he needs to have sex with them as well as hard training. Yes, his mission is to train them (sexually?) and make them great heroines!