An office lady who looks down on a man who spends all his time on horse racing and neglects his work. He makes her his target for revenge. The man prepares an "ovulation inducer for horses" to make horses go into heat. If it works on horses, which weigh ten times as much as humans, it must work on humans too. After drinking coffee mixed with the drug, the office lady enters a state of arousal beyond the man's imagining. She spontaneously takes the lead in a cowgirl position, shaking her hips violently. She doesn't care that it's raw sex. With her pussy filled to the brim with creampie semen, she engages in intense cowgirl riding. A trainer then gives her his seal of approval, stating, "She is a breeding mare of an incredibly high level."