A/N: This is a story written for the The Mirror of Erised Challenge on HPFC. This is what I think would happen if Colin Creevey came across the Mirror of Erised just before the Final Battle.
Colin Creevey ran up the stairs to his position on the third floor. He was feeling mostly excited and a bit apprehensive. He wasn't ashamed about that, though. He may be in Gryffindor, the house renowned for its bravery, but this was still war. He felt he had a right to be nervous. He was supposed to go with the other underage students but Hogwarts was his home too and he would defend it with the others; who cared if he was underage. Colin only hoped Dennis would be safe and that he hadn't thought of staying back; it was too dangerous for him to be here.
As he raced across the room to the window where he was supposed to attack the enemy from above, he spotted a flash of something white in the corner. He looked over and saw that an object in the corner was reflecting the rather small amount of light coming in through the window.
Colin walked hesitantly towards it, mindful of the DA meetings a few years ago. Once he stood in front of it he realized that it was a mirror. He read the inscription over the top: Erised stra ehru oyt ube cafru oyt on wohsi.
Colin looked into the mirror and gasped, whirling around. His worst nightmare: Dennis was here with him. He opened his mouth to yell at him and paused. His brother wasn't standing there behind him.
Turning back to the mirror he realised something that he had originally missed: Dennis was in their bedroom. He took a step closer and peered hard into the mirror. Dennis was safe in their bedroom back at home and Colin was with him. They looked to be a bit younger; before they had even heard of Hogwarts. Both their parents were reading them a story. They looked happy together.
He smiled at the mirror and touched the surface before a bang had him running back to the window in time to see giants emerge from the forest. He started casting spells down at the Death Eaters below; nothing too damaging in case of friendly fire. A giant spotted him and he had to jump back out of the way or risk being knocked down with the rest of wall onto the ground below. His lookout destroyed, Colin ran down the stairs to help defend Hogwarts. He paused at the top of the staircase and sent a prayer to whoever was listening.
Please let me go home. Please let us win. Please let Dennis be safe. But, most of all, please let my family know that I love them.