During the summer vacation, I was taking care of the children at my older brother's busy, dual-income household. My older sister-in-law, Fumika, had returned to work after her maternity leave, but since she was still anxious about leaving the kids with others, she had me do it. Fumika is a very beautiful and kind person, and honestly, I envy my brother. However, she is also a bit dreamy, or perhaps a little scatterbrained. It's like that even now. Despite me being her brother-in-law in the same room, she starts nursing without any pretense. 'Lately, my breasts have really built up... they're super full.' She doesn't seem to notice my gaze fixed on her breasts at all. With my arousal reaching its peak, I suddenly blurted out, 'O-oh, let me drink some milk, too!' Of course, it didn't end with just nursing... From there, a life of having sex while drinking Fumika-san's milk began.