"I'm Shadow the Hedgehog, and I made a promise that I intend to keep! With the power of these emeralds, Black Doom and his army are finished! This is who I am!"
The Black Arms invasion of Earth turned out to be a disaster, G.U.N.'s defense held them off long enough for Sonic and his friends to kick them to the curb. Black Doom had no choice but to call his remaining forces back to the Black Comet, but it couldn't end there. If left alone, the Black Arms would no doubt lick their wounds and launch a second campaign. Sonic decided to act as the vanguard of an assault on the Black Comet, so he gathered his companions and made for orbit. Shadow, sensing the remaining Chaos Emeralds on board the comet, joined Sonic in his gambit.
On the way there, memories of a certain individual resurfaced in the black hedgehog's mind. This person held great value to him fifty years ago; Maria Robotnik. She was Gerald's granddaughter, and Shadow's closest friend. Confined to the Space Colony ARK due to medical difficulties, Maria thought of how lucky people on Earth must be to have the freedom she didn't, and how little they appreciated it. Despite her difficult life, Maria never let anger and cynicism defeat her. She always had love to give, and hope for humanity. In her last moments, Maria begged Shadow to never give up this hope, to give them the chance they need to find happiness.
With Maria's wish weighing heavily on his mind, Shadow wasted no time in fighting through the Black Comet to Black Doom's inner sanctum. Even Sonic had a hard time keeping up with him. The Black Arms fortified the path to the inner sanctum, but they couldn't even slow the two hedgehogs down. There was more at stake than his memory or the Chaos Emeralds, Shadow had a promise to keep. Black Doom didn't even so much as blink when Shadow and Sonic reached him. It didn't seem as if the alien warlord could even feel fear, Shadow had every intention of correcting that. The fight was long and destructive, but Shadow thought of Maria, the love she felt for him and all who lived on Earth. These feelings amplified his powers with positive chaos energy, giving him the advantage he needed to overcome Black Doom and destroy him, claiming the last of the Chaos Emeralds in the process. Sonic, who let Shadow have his way, couldn't have been more proud.
Black Doom's death made G.U.N.'s following assault all the more easy. The Black Comet was destroyed by Shadow and the war finally came to an end. Across the planet, parades filled the streets and fireworks lit up the night sky. Though there was still some rebuilding to do on the United Federation's part, humanity as a whole could finally sigh in relief for the time being. The President personally thanked Shadow for his heroic efforts, and Sonic chose to keep away from the spotlight this time. This was Shadow's victory in more ways than one. The Commander of G.U.N., who previously held animosity towards the black hedgehog, offered him a position as an agent of G.U.N. Seeking to keep fulfilling Maria's wish, Shadow accepted.
Remembering his relationship with Maria also reminded Shadow of his grief over her death. Though he hid it, he also wanted to do something about it. The black hedgehog reconnected with Rouge and Omega and reformed Team Dark. Not only would he have help in protecting Earth, but also a means to fill the void left by Maria. He would never admit that last part though. For the first time in what felt like an eternity, Shadow allowed himself to smile when nobody was looking. He didn't realize how much he missed Rouge and Omega's company. Though he didn't consider himself a spiritual person, Shadow could swear he felt Maria happily watching him.
Shadow found more than a purpose. At last, he found peace.