Shiiba Mai, a fit woman with an irresistibly alluring, muscular physique and a large, shapely butt, NACR-859

The older sister trains at home. The younger brother has always harbored desire for her, but as she shows off her physique, displaying her well-toned buttocks while training, he gradually begins to look at her with lustful eyes. One day, he accidentally discovers his sister masturbating in her room, and then…