Imouto no Sausage

I'm Yui. I'm just a normal girl who really loves her big brother. When I'm alone with my big brother my heart always beats really hard. I wake my sleepyhead brother up in the morning and we eat together and go to school together. Tee-hee, it kinda makes me feel like we're newlyweds! But then one day I noticed something.. There was a sausage growing in my pants! It got all big when I touched it, and when I touched it some more it got all hard! What's going on? What should I do!? I can't tell my friends about this. Hey, big brother, look in my panties...do you see anything weird?