We've been step-siblings for 12 years. With our strict parents away, Izuna started wearing shorter skirts, doing bold makeup she never used to, and stopped changing out of her uniform. She developed bad habits—constantly crossing and uncrossing her legs, flashing her panties. When we were finally alone together again, we talked about love and romance, and I began feeling something shift. Later, while I was masturbating in my room, she secretly watched me. That's when she said, "Big brother, stop treating me like a child." Those words left me blank-minded, and soon after, I crossed the line.