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 G-merl, who is a powered-up form of the robot G-merl.
After G-merl and Dr. Eggman were defeated by Sonic in their encounter, the prescence of the Chaos Emeralds caused G-merl to go haywire and charge at Sonic, causing him to drop the Emeralds. G-merl then used their powers to transform into Ultimate G-merl. 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 G-merl 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, who is implied to have brought him to safety, Sonic headed out himself to search for new adventures. Meanwhile, G-merl 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 G-merl albeit with a more friendlier personality and G-merl 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.