Aries no Otometachi

After living abroad in Paris, France, Mizuho Kaoru returns to Japan to attend an elite private high school. Together with her beloved horse Electra, she joins the school's equestrian club, where she proceeds to distinguish herself as an Olympic-level rider, much to the jealousy of her teammates and some of the teachers at the school. Her only friend at the school is fellow classmate Kubo Emiko, who is part of the school's Drama Club and an equally distinguished performer.
Although only a year separates the two friends, they were born under the same horoscope sign as Aries and have an uncanny kindred spirit. It is not until later that we discover that the two high school friends not only share the same father but also share a dark family secret that will soon shatter their individual worlds apart.
(Source: DramaWiki)
~~ Adapted from the manga series "Aries no Otometachi" (アリエスの乙女たち) by Satonaka Machiko (里中満智子).