Hyakuya Sect

The Hyakuya Sect「百夜教」also referred to as the Brotherhood of a Thousand Nights before the Apocalypse, was a religious organization said to have been the largest of all the magical syndicates in Japan. They play a prominent role in the Seraph of the End: Guren Ichinose: Catastrophe at Sixteen light novel series.

History
For many years, the Thousand Nights fought with the Order of the Imperial Demons to control the reins of power in the country. However, after World War II, they gained the support of the United States and ever since then, were the dominant syndicate in Japan. The Thousand Nights had deep ties to Japan's political underbelly. Their power was far-reaching as nearly ever major politician relied on their support to stay in power. Few members of the general population knew of them, but they ruled the country from the shadows. They would stop at nothing to gain power and influence, which include murder, kidnapping, starting wars, and experimenting on humans to get it.

The Thousand Nights were infamous for running orphanages as a way to collect children with special gifts for cruel experimentation. When they found a suitable test subject, they would kill the parents and bring the child to one of their orphanages for grueling experiments. In particular, they were interested in the "Seraph of the End." Other experiments include giving their soldiers the ability to shoot and manipulate chains from their bodies and creating the Horsemen of the Apocalypse.

The Thousand Nights group in Japan was believed to have been wiped out by Krul Tepes along with all of their guinea pigs who possessed the seraph gene. However, she saved the children from at least one orphanage in Shibuya and raised them in Sanguinem, and two of those children were seraphs. Additionally, a few other seraph children had survived the Apocalypse. Kureto Hīragi claims they were an even more depraved organization than the Japanese Imperial Demon Army.

Known

 * Saitō
 * Unnamed Member
 * Mahiru Hīragi (defected and deceased)
 * Unnamed soldiers and scientists

Orphans
Note: They eventually change their surnames to "Hyakuya." Yu even confesses to forgetting his original surname.
 * Yūichirō Amane
 * Mikaela Shindo
 * Akane Iida
 * Junji Haiyama (Adopted by Miyuki Yamada (Mahiru Hīragi))
 * Yuki Endo
 * Chihiro
 * Kōta Hyakuya
 * Ako Hyakuya
 * Fumie Hyakuya
 * Taichi Hyakuya

Trivia

 * Saitō and Mahiru are the only known members of The Thousand Nights. The whereabouts of the main rulers of this organization are still unknown. However Saitō took over as the other scientists and soldiers simply obeys him, such as capturing Yu and destroy the JIDA.
 * Most of the orphans who resided in the Hyakuya Orphanage were either abused and/or abandoned by their parents and families there for unknown reasons though in Yūichirō's and Mikaela's cases, it was because they possessed the Seraph gene that the Brotherhood coveted for their experiments.