Oku-sama wa Dildo Ball ni Goshuushin

A married woman who loves dildo masturbation.
She was intrigued by the dildo balls she saw in an adult video and decided to make her own using a balance ball and a dildo.
When she actually tried it, she found that the position of straddling the ball made it easier for her to move the dildo in and out of herself and she became hooked on its effectiveness. As the ball bounced, her large breasts bounced, too, and she moved her hips faster and more vigorously with the dildo ball masturbation.

(Source: DLSite, translated)