At the time, the Emperor attended a reception hosted by the King for Heads of State and Official Overseas Guests at Buckingham Palace. This took place on 18th September, the evening before the funeral.
The planned visit for late June is in fact a rescheduling of a Covid-hit visit planned for Spring 2020. With so many difficulties taking place in relation to the health of the royal family, the King will no doubt be delighted to for an opportunity to return to full-scale royal duty. Where better to do so than at a state visit of an important partner like Japan?
It is likely that the visit will include strategic discussions, a guard of honour and a processional element, a number of informal and charity-based commitments and a state dinner. All eyes will be peeled for the splendour of the dinner, after the showstopping gala during the visit of South Korea last year.