Rokutousei Spica

Rokutousei Spica (六等星スピカ) is a manga series by Akira Onodera. It was serialized in Asuka (Monthly).

Plot
Supika studies at a school that teaches the magics of astrology and astronomy. Astrologers like Supika can use three magic items, a sun, moon, or star. Supika uses the star Spica (Virgo's brightest star), which is the most powerful item she can use at her level. In the school, however, women are stuck as third class students--they aren't allowed to reach the higher levels boys can. Of course, Supika doesn’t really agree with the obsolete rule and tries to get more powerful in order to become first class. Amano, the son of the principal, doesn’t agree with Supika’s free spirit and tries to stop her from becoming a first class astrologer...