Everything in this story will be pretty much canon, except for the OC I snuck in here, and everything she gets involved in, and for the ending. No spoilers, though, of course.
It was Fred and George Weasley's first year attending Hogwarts. Of course, neither of them were worried or nervous. They had both heard about the wonders of the school from their older brothers, Bill, Charlie and Percy. The two identical boys made their way through the train, in search for a free compartment. After a while of searching, they came across a compartment with a small girl with jet black hair whose face was towards the window. The twins announced their presence by clearing their throats. After jumping, the petite girl turned her heads towards them. When she faced them properly, they took note of her small features. Her eyes, nose, and mouth fit perfectly on her small, round head. "Do you mind if we sit? There's nowhere else..." One of them asked politely as they could. "Oh, no, go ahead," she replied with a small smile as she watched them take a seat facing her. "I'm Fred - he's George. Though, I'm not sure that matters, since you'll probably mix us up anyway." The girl replied with a chuckle. "I'm Olivia." And like that, the boys quickly became close with the small girl named Olivia. They learned more about her - she was a half-blood, her mother was a Muggle from somewhere in South Korea, and she moved to London where she met her father. The compartment with the three was loud with roars of laughter, and their train ride soon came to an end.
The three lined up with the other first years, after having changed into their robes, and waited to get to a boat. They shared one and ventured across the water and to the castle. "It's better than dad said it was," the boys could hear Olivia whisper to herself with excitement. They all stared in awe in every direction. Hogwarts was beautiful, and the lights showed it perfectly. The water reflected the lights from the castle, and it was too much for Olivia to take in. Fred turned around to look at her, and he could see her child-like grin in the lights.
When the last of the first years reached the castle, they all entered the great hall. Eyes widened, and jaws fell open while amazed whispers filled the giant room. The older students watched as the first years made their way up to the sorting hat. After Professor McGonagall explained the sorting ceremony, she began to call up names. After a few names were called, Fred and George both blanked out - until Fred's name was called. The redhead made his way up to the Sorting Hat. Almost immediately after sitting down, he was put into Gryffindor. He took a seat across from his brother Percy, followed by George, who was sorted just as quickly Fred. George had blanked out again, but was disrupted when Fred had nudged his side. He caught the next name that McGonagall had called out. "Olivia Oh," and the boys watched as their new friend had the Sorting Hat placed on her head. It took it's time with her, muttering about her brains and her bravery. Eventually, her nerve won, and she was placed in Gryffindor. "Welcome to Gryffindor, my dear Olivia," George chuckled, as she took a seat across from him. Their first night with stuffed stomachs, and a very long talk in the common room before they were forced up to bed. This was a very eventful first day at Hogwarts.