It's the 25th year of the Taisho Era in Imperial Tokyo. Kuze Tsugumi, daughter of aristocrats, agrees to be married to save her family from decline. But before she goes through with it, her younger brother Hitaki gets her involved in an incident caused by a "maremono," a type of book that casts a great influence on whoever reads it. As a result, Tsugumi gains the power to see "aura," a light that represents the emotions that dwell within a maremono. This is the story of a woman whose destiny seems to sway up and down, as if on the delicate balance of a scale.

Die Geschichte von Libra of Nil Admirari spielt in der Taisho-Ära, zu Beginn des 20. Jahrhunderts – die jedoch nicht wie im realen Leben nach 15 Jahren endete, sondern 25 Jahre andauerte. Um ihre in Ungnade gefallene Familie zu schützen, entscheidet sich die Tochter der Familie, einen Mann zu heiraten, dessen Namen sie nicht einmal kennt. Doch noch bevor es zu ihrer Heirat kommt, begeht ihr kleiner Bruder, inmitten eines seltsamen Feuers Selbstmord – in seinen Händen, ein altes Buch.

Kurze Zeit später erscheint vor Tsumugi, so der Name des Mädchens, eine seltsame Organisation namens „Fukurou“ und erzählt ihr, dass es mehrere Bücher, auch Maremono genannt, gibt, welche einen großen Einfluss auf diejenigen ausüben, die es lesen. Das ist aber längst nicht alles, denn seit dem Vorfall mit ihrem Bruder, besitzt Tsumugi die Fähigkeit, die Aura ihres verstorbenen Bruders zu sehen.

For high school students like Shouichi Kamita, university entrance exams and the future are common concerns. It is also during this time in life that a mysterious emotion that vexes people of all ages may begin to weigh upon one's mind—love.

At this point in his teenage years, Shouichi finds three girls he could see himself having a future with: the ever-cheerful Hikari Tsuneki, who teases Shouichi without mercy, but actually has a softer side; the competitive gamer, Tooru Miyamae, who has difficulty communicating with others; and Shouichi's childhood friend, Kyouko Touno, the sometimes immature shoujo manga enthusiast. Seiren follows Shouichi's relationships with these three girls across three separate arcs, as their feelings grow from mutual interest and blossom into something more beautiful.