Abdication of the throne (退位)
Abdication of the throne implies resignation by a monarch such as an emperor or a king from his or her position. Also, unless the monarchy is abolished, for example by a revolution, the position is automatically passed on to the successor.
Transferring of a monarch's position that accompanies abdication of the throne is called 'abdication.'
Japan
In Japan, the oldest example is that of the Emperor Kogyoku handing down the Imperial Throne to his younger brother, the Emperor Kotoku, and there exist 89 examples (*) of abdication (because of the unification of the Southern and Northern Courts the throne was passed down to the Emperor Gokomatsu twice). An emperor who abdicated was called Daijo Tenno (Joko, Retired Emperor).
* While 3 examples from the Northern Court (Japan) are included, the 4 examples of the Emperor Junnin, the Emperor Chukyo, and the Emperor Kogon and the Emperor Suko of the Northern Court, which effectively were dethronement, are excluded.
Following the Heian Period, a system of ceremonies centered on two rituals, one in which the abdicating emperor issued an edict proclaming his abdication, and the other in which the Kenji (the Sacred Sword and the Sacred Jewel) were passed down to the successor (the new emperor) became customary.
According to the Imperial House Act established during the Meiji Period, succession to the Imperial Throne presumes the death of the Emperor, and therefore, it is interpreted that, under the existing law, abdication is not possible while an emperor is still alive (it is said that, when the Imperial House Act was established, the reason for this limit was to prevent the Emperor from abdicating and thereby pressuring the government if there was a confrontation between the Emperor and the government. Also, it is said that Emperor Showa considered abdicating after World War II, but because of opposition from all sides this issue faded away).
There are views that say abdication before death should be allowed, based on respect for the Emperor's free will and the existence of former examples, but there are strong opposing views because of the issues of how the Emperor should be treated after his abdication (financial matters and issues on his position in the political administration. The latter, in particular, is a problem of political administration by the retired emperor), complications in the succession to the Imperial Throne, and the possibility of the extinction of the Imperial Line due to the lack of a successor.
United Kingdom
King Edward VIII is the only king from the House of Windsor to have abdicated. In order to marry a divorcee, he abdicated in 1936, less than a year after he ascended the throne. It is well-known as love over his crown.
Treatment after abdication
In cases where abdication is accomplished relatively peacefully, the former monarch and his family members are often guaranteed treatment with the same degree of honor as before.
The Japan-Korea Annexation Treaty (1910): The Emperor of Korea and the imperial family were entitled to suitable honorific titles, authority and honor, and in accordance with the Act, which acknowledges the former Emperor of Korea as King, establishes titles for each prince, future successor, and the empress, and treats them with courteous reception, the status of 'king' was granted to the former emperor of Korea, a system known in Japanese as Okozoku. This status was lost in 1947 when the Constitution of Japan, which abolished the aristocracy except for the Imperial Family, came into effect.
Conditions for the favorable treatment of the Emperor of the Qing (Shinshitsu yutai joken) (1912): After his abdication, the last emperor of China was given the honorific title 'Emperor Daishin' and received the same treatment as monarchs of foreign countries. It was later annulled.
Abdication of the throne by Edward VIII (King of England) (1936): He voluntarily abdicated as 'King of Great Britain, Northern Ireland and the British Dominions beyond the Seas, Emperor of India.'
After his abdication he was conferred the dignity of peerage as Edward VIII.