Both of our parents work and are often away from home. That's why I've been teaching my sisters all sorts of things since they were little. Of course, the naughty things that would drive our parents crazy if they found out. They've become super capable, naughty sisters who will suck me off as soon as I call out to them, regardless of the time, place, or situation. Thanks to that, they're now obedient and will even have sex with me whenever they feel like it. However, I didn't expect that they've become a bit of a sex monster thanks to their excessive erotic education, but they're still useful as a masturbation toy!