Today my girlfriend went on a trip with her family so she asked me to drop her off at the train station. Because we are forgetful, both of us hurried back to her house to pack her luggage. This was also the first time I met her older sister, who has a huge pair of breasts and wasn't wearing a bra. After dropping off my girlfriend at the train station, I remembered that I left my bag at her house. When I went back inside, I saw her sister's giant bra that she had forgotten. Thinking no one was home, I decided to 'take care of business' right there but her sister caught me in the act. I thought I would be scolded for being a pervert, but no, she wasn't mad at me at all. To my surprise, she offered me water, allowed me to take a photo of her breasts through her shirt, then gave me a massage, squeezed and fondled her bare breasts, and proceeded to have sex with her! For the next three days, we stayed together, having sex with each other until my girlfriend returned.