Shoujyuku (松塾) was an institute built in Shishou, San Prefecture in Baku Province in the kingdom of Kei during Tatsu-Ou's reign. The institution emphasized teaching wisdom rather than strictly knowledge and a number of graduates from Shoujyuku were seen as heroic officials in the eyes of the citizens. A number of people in Kei of consider the whole story of Shoujyuku a mere legend after it was destroyed.
It is believed that Enho once taught there, though he had retired by the time Saibou and Koukan were students. The headmaster at the school during Koukan's time at the Shoujyuku was once a student of Enho and had brought Koukan to meet Enho several times. The Taisai, the Palace Administrator for the Ministry of Heaven and Seikyou's primary opponent in court, was also supposedly a graduate from the Shoujyuku.
Many students of the Shoujyuku were known to criticize the systems in Gyouten and Wa Province. During the reign of the false queen Joei, the Shoujyuku was burned down to prevent students from spreading information that Joei was not the legitimate ruler of Kei and the corrupt officials responsible for the act blamed a refugee from Takuhou. Seikyou regarded the Shoujyuku as a threat to his power because officials from the Shoujyuku would not hesitate expose his corruption to the new ruler of Kei.
The group led by Koshou and Sekki use the legend of the Shoujyuku as a pass code for their members. After members discreetly clasp hands to reveal the grey rings they are wearing, one member will reveal that they are a friend to the cause by remarking they are from "Shikin in San Prefecture in Baku Province", a reference to an old place name from the reign of Tatsu. The other member will respond by introducing themself as "Otsu-etsu from Roushou"; both "Otsu-etsu" and "Roushou" refer to a flying sage who lived in Shikin.