When Rika Kayama attended a violin concert at a Tokyo music hall in February last year, she was stunned to find a certain famous face in the crowd.

It was Crown Princess Masako, who had long avoided public appearances because of her battle with adjustment disorder, a mental condition characterized by strong emotional and physical reactions to stressful events.

Kayama, a psychiatrist and professor at Rikkyo University, has authored several books on the Crown Princess and her mental illness.