Game concept · All Under Heaven
Cloistered Emperor
The game also links it as Cloistered Emperor's, Jōkō, Jōkō's.
From the game's encyclopedia
A Cloistered Emperor is a retired Ten'nō who govern as de facto Ruling Regent for the reigning Emperor.
To become Cloistered Emperor, an Emperor must abdicate the Chrysanthemum Throne and become a Monk.
The game's text for patch 1.20.1.2. Words in blue are entries of the encyclopedia: hover one to read it, as in the game.
Cloistered Emperor is an entry of Crusader Kings III's in-game encyclopedia (All Under Heaven). The game explains it: "A Cloistered Emperor is a retired Ten'nō who govern as de facto Ruling Regent for the reigning Emperor." It is part of Ruling Regent. The game also links it as Cloistered Emperor's, Jōkō and Jōkō's. Patch 1.20.1.2, from game/common/game_concepts/tgp_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
Source: game/common/game_concepts/tgp_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.