Susanoo came in many forms. From the most basic version, which only manifested arms and ribs for defense, to the final complete form that could fly through the sky and burrow into the earth, there were several stages in between—not to mention certain special cases. Madara's "Tailed Beast Disaster," Sasuke's curse-mark version infused with natural energy, and the strongest version that perfectly fused the chakra of all nine Tailed Beasts.
Special cases were exclusive perks for cheat-code players. Generally speaking, a civilian Uchiha like Izuna, who had no powerful father, only needed to practice ordinary Susanoo. The complete form was beyond him.
There was no other reason: the requirements were simply too harsh!
To activate the complete Susanoo, one had to push the Eye Power of the Mangekyō Sharingan to its limit while possessing enormous chakra reserves. But training the Mangekyō's Eye Power to its limit was basically a joke, because the Mangekyō had an utterly terrible setting: use it too much, and you went blind.
Going blind in the Sharingan meant losing the key to activating Susanoo. Unless one could force the door open through brute strength, the only option was to sit down and chat with Madara about dreams. Dreams had everything.
Izuna had been unable to activate the complete Susanoo while alive, but that no longer mattered. After Impure World Reincarnation, he could use it. With unlimited chakra and no concerns about blindness, activating the complete Susanoo came naturally.
The frustrating part was that he, Uchiha Izuna, the renowned second-in-command of the Uchiha during the Sengoku era, had never reached the complete form even in death—yet Duke, an outsider, had achieved it with ease.
Chakra flowed and burned like endless green flames. After taking humanoid form, the chakra solidified into substance. Duke's Susanoo was taller, stronger, thicker,