Because the house is too small, I still share a room with my sister. My sister goes to a school for sluts, so of course her friends are sluts! So every time her friends come over to my house, they talk about how they're sluts, which is too much for me, a college entrance exam student! That slutty woman teased me and said, "You can do it up to B!" So I licked her nipples enthusiastically, and my sister's friend, who had never experienced careful foreplay, came many times, and she wasn't satisfied with that and asked for a deep kiss, and then...