Mitsuzumi Ijuin was born in Shimotsuke Province in Tochigi Castle, to the Yamanouchi branch of the Uesugi clan. Ijuin was the son of Kagekaktsu Ijuin, a Yamanouchi retainer. He was the brother of Mitsumasa Ijuin and Mitsuyama Ijuin. Mitsuzumi drew his first sword in 1545 during the Siege of Kawagoe Castle, where he fought under Norimasa as an adjutant. Mitsuzumi became the guardian of Tochigi Castle following the siege, as Norimasa cut his losses by retreating from the Hojo advance. Mitsuzumi was besieged in Tochigi Castle by Hojo siege engines under Ujiyasu Hojo himself, and he was slain in the castle when it was captured.