(From left) Empress Masako, Emperor Naruhito, Princess Aiko, 2011
Who is a Kotaishi (皇太子) now?
Nobody is. Prince Akishino(秋篠宮) is a Koshi(皇嗣) but not a Kotaishi (crown prince) because he is not Emperor Naruhito’s child but the younger brother. On The Imperial Household Agency(宮内庁, Kunaicho) website, he is called Crown Prince, but it’s technically wrong. (https://www.kunaicho.go.jp/e-about/genealogy/koseizu.html)
What is a Koshi (皇嗣)？
A Koshi is just the first person in the line of succession. It will be changed depending on the situation. The person who is second or lower line of succession is not a Koshi.
Strictly speaking, a Kotaishi is an heir apparent: the person who is first in the line of succession and cannot be displaced from inheriting the birth of another person.
On the other hand, A Koshi is an heir presumptive: the person who is first in the line to inherit a title but who can be displaced the birth of a more eligible heir.
Besides, a Kotaishi is not allowed to renounce the status of a member of Imperial Family, either by the will or by a resolution of the Imperial House Council(皇室会議, Koshitsu Kaigi), but a Koshi is allowed to do it.
A Koshi is not simply a Kotaishi, because there is the basic view that a direct line (from parents to a child) of succession to the imperial throne is the way it should be.
The difference between Kotaishi and Koshi is quite significant!
By the way, the ceremony, Rikkoshi no Rei(立皇嗣の礼) has postponed, which was going to take place on April 19th.
What is Rikkoshi no Rei?
Written by Mamegashi (from Aichi)
(文責 愛知県 マメ菓子)