The King will toast his visitors at such events, often in their own language, and make a speech in honour of his guests.
The emperor will then reply.
Prime Minister Rishi Sunak and Labour leader Keir Starmer will be at the state banquet, on Tuesday evening, in one of the last such formal occasions before next week’s election.
The following night, the two party leaders are in a head-to-head TV debate.
The emperor and empress’s programme of visits over the next few days will include Westminster Abbey, the Francis Crick Institute, Kew Gardens and the Royal College of Music.
They will lay a wreath on Elizabeth II’s tomb, in St George’s Chapel, Windsor.
And on Friday, after the state visit has ended, they will make a nostalgic return to their former colleges at Oxford University, where they were both students.