栗原海里（和气杏未 配音）是一位非常善良的高中生，因为在所有方面都比别人强一点点，所以海里的高中生活过得并不是那么的顺利，周围的人总是和她保持着距离，这让海里倍感孤独。一场意外中，海里遭遇了事故，转生来到了异世界中，她向神明许愿，希望在这里自己能够成为一个所有数值都是平均值的普通少女。
口嫌体正直的傲娇少女烈娜（德井青空 配音）、经常被误会是男性的女骑士梅维丝（内村史子 配音）、身材娇小个性温和的珀琳（田泽茉纯 配音），在这里，海里很快就结交了一群朋友们。随着时间的推移，海里渐渐发现，绝对平均的数值对于她来说，竟然成为了一种优势。

本作是「赛马娘 Pretty Derby」的衍生作品，全篇将以原创故事展开。赛马娘们魅力四射的宝藏泡面番。不仅有竞速、演唱会，更有各具特色的赛马娘们的可爱校园日常。那么，冲呀！

Famous racehorses that have left behind worthy legacies, unique as they can be, are reincarnated as horse girls in a parallel world. In this life, they start their journey anew as they continue to race and perhaps relive the success they once lived through.

Aspiring to become the best racehorse in Japan, a horse girl named Special Week moves to Tokyo to enroll in the Tracen Academy—an institution that nurtures horse girls like her to become better racers. There, Special Week witnesses the sophisticated running style of Silence Suzuka and is inspired to become a racer like her. Shortly after, Special Week finds herself recruited into Silence Suzuka's team, Spica. From there, she begins her path to the top—one lap at a time.

Single father Kakushi tries to hide his job as an adult manga creator from the daughter he adores, a scheme that gets more elaborate as she grows.