Rika Fujishita is a busty and proud mother, but due to her large chest, she struggles to find bras that fit and usually goes without underwear. One day, her teenage son begins to notice his mother's swaying breasts, and Rika becomes aware of his gaze, recognizing his innocent curiosity. Seeing her son helping with household chores, she feels maternal warmth and tenderness toward him, wanting to nurture his growth. Gradually, the bond between mother and son begins to shift into something new.