Mitsukuni grew up quickly and healthily. In 1632, when Mitsukuni was 5 years old, he was officially acknowledged as a child of Yorifusa. Mitsukuni moved to the Mito Castle. He was smart and good at martial arts. He had a good reputation.
The third Shogun Iemitsu was a close friend of Mitsukuni's father Yorifusa. Yorifusa was an uncle of Iemitsu but Yorifusa was just one year older than Iemitsu.
Iemitsu had experienced a severe family battle over the succession to the Shogunate. Therefore, when Iemitsu found out about Mitsukuni's reputation, he advised Yorifusa to declare his heir soon.
According to the advice, Yorifusa let his vassal, Nakayama-Bizennokami, to go to Mito to check on Mitsukuni. Nakayama-Bizennokami had also seen Yorifusa's other children.
Mitsukuni was smart and considerate. Therefore, Nakayama Bizennokami recommended Mitsukuni as the heir of Yorifusa.
According to the recommendation, Yorifusa declared Mitsukuni as his heir.
Photo: Edo Tokyo open air Architectural Museum