Empress Emerita Michiko, wife of Emperor Emeritus Akihito, turned 89 on Friday.
An event to celebrate her birthday will be held in a simplified manner at Sento Gosho for the second consecutive year. The number of participants is expected to increase from last year.
She currently lives in Sento Gosho after she moved to the Imperial residence in Tokyo's Minato Ward one and a half years ago.
She had refrained from going out during the COVID-19 crisis, but has been taking a more opportunities to do so since the government in May lowered the classification of COVID-19 to Class 5 under the infectious disease control law, matching seasonal influenza.
At Sento Gosho, the former empress enjoys observing seasonal insects and flowers and continues to take a walk in the morning and evening and read aloud books after breakfast.
But the 89-year-old Emperor Emeritus is concerned about the health condition of his wife, whose psychical strength is deteriorating, her aides said.
She has often been developing a fever in the afternoon for over three years. Her brain natriuretic peptide level, a diagnosis index for heart failure, is still above normal.
In August last year, she was diagnosed with deep vein thrombosis after a clot was found in her right calf. But her condition is stable as she exercises and drinks plenty of fluids.