Nonaggression (ノンアグレッション,Non'aguresshon?) is the ninth and true final Zone in Sonic Advance 3, unlocked if all of the Chaos Emeralds have been found, Sonic is leader, all characters have been unlocked and the final boss is rebeaten. It features the final fight against Ultimate Gemerl, who is a powered-up form of the robot Gemerl.
After Gemerl and Dr. Eggman were defeated by Sonic in their encounter, the prescence of the Chaos Emeralds caused Gemerl to go haywire and charge at Sonic, causing him to drop the Emeralds. Gemerl then used their powers to transform into Ultimate Gemerl. Before leaving, he used one of his "arms" to grab Eggman and throw him into Sonic. When he recovered, Sonic then used the Chaos Emeralds to become Super Sonic and teamed up with Eggman to bring the out-of-control Gemerl down.
At the end of the fight, Sonic passed out in the following explosion, but woke up back home and found himself surrounded by his friends who had awaited his return. After seeing Eggman leaving, Sonic then headed out himself, searching for new adventures. Meanwhile, Gemerl reverted back to his normal form and lands at a beach who was eventually found by Cream. She took the damaged robot to Tails who repairs Gemerl albeit with a more friendlier personality and Gemerl quickly became friends with Cream.
The name "Nonaggression" is a reference to how Sonic and Dr. Eggman are working together instead of fighting each other.