My step-sister, who was born from my parents' remarriage, is a gloomy otaku who can't get along with anyone! What's more, she brought her friends over for a girls' night out today! I sneak a peek into her room and... she's looking at erotic manga with her hidden huge breasts exposed!? Huh? Do they all have huge breasts? They're looking at it with such lewd expressions that I can't help but get a full erection! When my step-sisters notice me like that, their lewd nature, which I had been holding back, is unleashed! The nasty...