Al notar que su tía no puede pagar las facturas, Peter decide buscar trabajo en cualquier lugar con el objetivo de conseguir dinero para ayudar a su tía, si bien el bugle le pagaba bien no era lo suficiente para las facturas de la casa, apesar de buscar por todos lados peter no encontraría como ganar más dinero para su tía, cuando estaba apunto de rendirse este ve en un periódico algo llamado "Carreras de umamusume" se trataba de chicas fusionadas con ADN de caballo que competían en una carrera como los caballos normales. en el periódico decía que buscaban entrenador para una umamusume, peter no estaría convencido un principio, pero al ver lo que le pagarían este decidió acceder, ya que con ese dinero podría ayudar a su tía con las facturas del hogar sin embargo no sabría que está decisión le traería a algo peor que un supervillano

One day, a man is reincarnated into the world of a game he had loved in his previous life-Uma Musume: Pretty Derby. And the one he is reborn as is his favorite character: the cheerful, peach-haired horse girl, Haru Urara. Determined to become just like the Haru Urara from the game, she works hard, and at Tracen Academy she meets a timid female trainer. Together, Haru Urara and her trainer grow, make many friends, and enjoy a bright, happy school life- Just like the Haru Urara from the game. In one race, Haru Urara loses. Yet even in defeat, she smiles brightly. Because she was satisfied. But one day, she sees her trainer in tears-and realizes her own foolishness. The trainer had truly, desperately wanted Haru Urara to take first place. She sincerely believed that Haru Urara's inability to win was her own fault. So, to never make her trainer cry again, Haru Urara begins to desire victory. She trains for the sake of winning, throws away the joy she once cherished, and thinks of nothing but how to win. And then... The peach-haired horse girl becomes a Demon King who dominates not only the races, but the spectators themselves. Disclaimer: this story by Glen Leastar/グレンリアスター, Am just Translating Original Title : 桃桜の魔王