Soccer player Hayasaki Ryoushirou returns home with a sports injury. When his four older sisters find little sister fetish material in his luggage, the only possibly therapy for his unacceptable (and non-existent) lolicon fetish is sex with his busty older sisters Yuri and Mio.
Marina and Airi's single mother has recently gotten married. Their new step-dad seems like he'll make a loving father. Like a really, really loving father.
