Yet under the male-only succession law, the toddler has a weighty destiny ahead of him.
He is third in line to succeed 75-year-old Emperor Akihito on the Chrysanthemum Throne behind his uncle, Crown Prince Naruhito and father Prince Akishino.
This explains why there is such interest in every little detail of his life in a country where there is a lot of enthusiasm for the imperial family.
During his third birthday, on September 6, the TV was filled with footage of the youngster, affectionately nicknamed "Yuyu," and "Yu-chan" by his parents, running into the arms of his father.
Admirers learnt that Hisahito currently weighs just over two stone and stands more a little more than three feet tall.
His favourite activities, reveals the imperial household are, of course, riding his tricycle and playing ball and chase. He can also eat and change his clothes by himself
Hisahito was the first male heir born in 41 years to the imperial family and his arrival was greeted with general rejoicing.
Until his birth politicians had been considering changing the male-only succession law, which would have allowed his cousin Aiko, Naruhito's daughter, to reign.