Choso means reaccession of retired emperors to the throne.
Emperors in Japan
Two emperors performed choso in the past; Emperor Kogyoku ascended the throne a second time as Emperor Saimei and Emperor Koken ascended the throne a second time as Emperor Shotoku.
Emperor Kogyoku stalled for time due to political speculation of his son Emperor Tenchi. Emperor Koken once transferred the throne to Emperor Junnin due to his political calculation, but took it back forcibly.
Emperor Godaigo was exiled to the Oki Islands due to the Genko War and Emperor Kogon (currently the Northern Court [Japan] Emperor) ascended the throne, but Emperor Godaigo who escaped from the Oki Islands and came back to Kyoto denied the enthronement of Emperor Kogon. Some think that this is chosa of Emperor Godaigo after Emperor Kogen from the viewpoint of orthodoxy of the Northern Dynasty. Since the Southern Court (Japan) is now considered to have orthodoxy, the enthronement of Emperor Godaigo was effective when he was exiled to Oki.
The enthronement of Emperor Kogon as orthodoxy was considered to be 'nonexistent.'
Emperors in China
In China, Busokuten enthroned in Tang and a nation was founded (Busokuten) in the end of the 7th century to the beginning of the 8th century, and Jungjong (Tang) and Yejong (Tang) were dethroned by Busokuten. They came back to the throne after the death of Busokuten. When Eiso (Ming) was captured by the Oyrat force in the Tumu Incident, the Imperial Court enthroned his younger brother (Kageyasutei) and imprisoned Eiso after his return. Eiso staged a coup d'etatand (Datsumonnohen) later and was coronated again.
Kings in Korea
When Goryeo came under the rule of Yuan (Dynasty) in the end of the 13th century to the middle of the 14th century, the throne was transferred to a crown prince or restored in line with the wishes of the Yuan imperial court. Because of this, the imperial court confused and reliance on Yuan increased, and the dynasty declined.