Kōryaku
Kōryaku was a Japanese era name of the Northern Court during the Era of Northern and Southern Courts after Eiwa and before Eitoku. This period spanned the years from March 1379 through February 1381. The emperor in Kyoto was Emperor Go-En'yū The Southern Court rival in Yoshino during this time-frame was Emperor Chōkei.
Nanboku-chō overview
During the Meiji period, an Imperial decree dated March 3, 1911 established that the legitimate reigning monarchs of this period were the direct descendants of Emperor Go-Daigo through Emperor Go-Murakami, whose Southern Court had been established in exile in Yoshino, near Nara.Until the end of the Edo period, the militarily superior pretender-Emperors supported by the Ashikaga shogunate had been mistakenly incorporated in Imperial chronologies despite the undisputed fact that the Imperial [Regalia of Japan|Imperial Regalia] were not in their possession.
This illegitimate Northern Court had been established in Kyoto by Ashikaga Takauji.
Change of era
1379, also called Kōryaku gannen: The new era name was created to mark an event or series of events. The previous era ended and the new one commenced in Eiwa 5.In this time frame, Tenju was the Southern Court equivalent ''nengō.''