To prepare for my exams, I moved in with my older brother. When I got there, my brother was gone, and my sister-in-law, Hikari, greeted me alone. She's always cheerful and kind, a beauty that's too good for my brother... I've secretly admired her since the first time we met. It seems my brother is away on a business trip for a whole week, leaving me alone with Hikari... Her revealing attire accentuates her already stunning breasts, and her innocent demeanor leaves me, a virgin, unable to focus on my studies... Then, with her words, "This is practice for when you have a girlfriend," I finally reach my limit...