Fushigi Yuugi Genbu Kaiden, Yuu Watase's 'prequel' to Fushigi Yuugi, was first published in Shojo Comic (Sho-Comi) in October 2003. It appeared in Watase's Perfect World from June 2004 to August 2008 and continued in Flowers and the inspired spin-off Rinka after an extended hiatus. Ten years after it's creation, the final chapter of Genbu Kaiden was released in February 2013. The series consists of 40 chapters (or 12 volumes).
The Universe of the Four Gods is a book from China. It was found and brought to Japan by Einosuke Okuda in 1923. It has the power to draw a reader into its story, thus making them part of the tale. Einosuke's daughter, Takiko, is pulled into the book and begins the journey that prefaces Fushigi Yuugi.
The Universe of the Four Gods is set in Ancient China (with liberal creative license). The land is divided into four main provinces, each at a cardinal point. The countries are ruled and protected by different beast gods who can only be summoned by priestesses from another world.
Hokkan, a cold, snow-filled nation in the north, worships Genbu. Genbu was summoned two hundred years ago (in the book) by Takiko Okuda. At the time, Genbu was considered a curse and feared by his people. Takiko was the first priestess to enter the Universe of the Four Gods and her necklace, a gift from the prophet Anru, becomes a Shinzaho necessary for future priestesses to have in summoning their respective gods.
Sairou, a mountainous, desert region in the west, worships Byakko. Byakko was summoned ninety years ago by Suzuno Osugi. Suzuno was the second priestess to enter the Universe of the Four Gods. A mirror she held during her summoning ceremony becomes another Shinzaho. Even though Byakko was called to service more than a century later, Suzuno was eight years old when Takiko left to summon Genbu. Time in the book of the Universe of the Four Gods flows faster than the 'real world'.
Kutou, marred with a history of battle and invasion, lies in the east and worships Seiryu. Seiryu was the third god to be summoned. He was brought forth by Yui Hongo. Yui enters the book at the same time as Miaka, Priestess of Suzaku. It is unclear whether or not Yui leaves a Shinzaho behind.
Konan, a forested, green country in the south, worships Suzaku. Suzaku was the last of the beast gods to be summoned. He was brought forth by Miaka Yuki. Miaka's Shinzaho is revealed in Fushigi Yuugi Eikoden as her and Taka's unborn child.
The section below contains spoilers.
For a spoiler-free summary, read the welcome message on the main page.
Fushigi Yuugi Genbu Kaiden takes place two hundred years before Miaka and the Suzaku seishi. It focuses on the northern province of Hokkan and Takiko Okuda, the Priestess of Genbu.
Takiko lives in the real world feeling unneeded and unwanted. Her skill with a naginata (a bladed-spear) sets her apart from female peers, and questions on her mother's health keep her distant and reserved. She isn't close with her father and resents his work in China. When Einosuke Okuda returns home, he brings back a mysterious book called the Universe of the Four Gods. Consumed with study, he ignores his wife and daughter. Soon after his arrival, Takiko's mother succumbs to tuberculosis and dies.
Furious at her father's seeming apathy, Takiko corners him in a tearful confrontation. She asks why he's never home and if his absense is her fault. He admits to wishing she were born a boy, leaving Takiko devastated.
Feeling orphaned, Takiko enters the book. She is dropped on a snowy mountaintop in Hokkan, where a girl is chained and set for execution. The girl is Rimudo Roun, one of the Genbu seishi. Rimudo is actually a man who transforms into a woman when using his celestial power.
Takiko's story is one of well-known tradgedy. In Fushigi Yuugi, Keisuke (Miaka's brother) and Tetsuya travel to Morioka to learn more about the Priestess of Genbu. They discover that the priestesses' father (Einosuke) killed his daughter (Takiko) to prevent her from being devoured by the beast god Genbu.
How Watase plays this out is something you should read for yourself.