Good luck attempting to travel internationally without a passport. You'll likely be stopped by airport staff before you leave your home country. Even if you manage to reach another nation, trying to slip past border control will result in grave consequences.
But for three people on this planet, passports are a non-issue when globe-trotting. These privileged travelers are Emperor Naruhito and Empress Masako of Japan, and King Charles III of the United Kingdom.
This unique rule harks back to earlier monarchs, including Queen Elizabeth II. The reigning UK monarch has a document issued in their name, ensuring a no-hassle international journey. However, this travel perk does not extend to their family members. For instance, Queen Consort Camilla, King Charles III's wife, still requires a diplomatic passport for her foreign ventures.
In Japan, a 1971 Ministry directive dispenses the need for passports for the Emperor and Empress because it just didn't seem right to make the direct descendant of the sun goddess Amaterasu go through typical immigration procedures like mere humans. (Like in the UK, this dispensation is exclusive to the monarchs, not extending to Japan's Imperial family.)
These unique travel arrangements necessitate detailed coordination between high-level officials from the countries involved. Sir Clive Alderton, the long-serving private secretary to King Charles III, takes charge of the UK monarch's travel logistics. In Japan, the Ministry pre-informs the destination country about the royal couple's arrival.
[Via Outlook India]