Before the era of ninja villages, Izuna was one of the five sons born to Tajima Uchiha. However, three of his brothers died at the hands of the Senju, leaving the second eldest Izuna and his oldest brother Madara. Alongside Madara, Izuna was considered one of the most gifted members of the Uchiha. Izuna often competed with his brother as training. As a child growing up during the war-torn era, Izuna once accompanied his father on a mission to kill Hashirama Senju, whom Madara — albeit unknowingly — had been meeting. Once there, Izuna and his father were confronted by Butsuma and Tobirama Senju, the latter of whom he acknowledged by name.
As Izuna clashed with Tobirama, unbeknownst to him, Butsuma had launched an attack at him, hoping to strike him down and gain an advantage at defeating the evenly-matched Tajima. This attack, however, was deflected by his brother Madara who had intervened between the two sides along with Hashirama. Izuna later showed shock when Madara noted that Hashirama was stronger than he was, but was later elated to see that his brother had awakened his Sharingan.