A/N: Since we all know there's no Cho in the third movie, we're all wondering how they're going to introduce her character in the fourth, right? ;) So… here's a (really really really short) idea from me…
The Beginning
A pretty Ravenclaw girl with long shiny black hair and sparkling brown almond eyes ran herself and her trolley through the magic brick barrier. Once on the other side, she stopped abruptly, preventing a crash with another person's cart, who had obviously just arrived breathless through the barrier as well.
"Sorry," she said, taking a glance at the tall, lean person.
"Quite all right," answered the bespectacled boy in a deep voice.
The Asian 15-year-old did a second take, cocking her head and looking at the boy. She grinned. "You're Harry Potter, aren't you?"
They boy called Harry, whom she noticed was kinda cute, looked back at her. "Yeah."
"Then you two must be Ron and Hermione," she continued.
"Um… yes. Bloody hell, you're good. How'd you know?" asked the boy called Ron perplexedly.
The girl rolled her eyes, laughing. "Let's just say the school hears a lot about you three."
The other female, whom she had called Hermione, backhanded her red-haired friend playfully. "Come on Ron. Get a clue."
"Oh. Right."
Harry finally said something else. He had noticed that the Asian girl was very pretty—she had a beautiful smile, beautiful hair, beautiful body… wait a minute. "Aren't you on the… Ravenclaw Quidditch team?"
"Yeah!" Now the girl was a bit surprised that Harry Potter had recognized her.
"So, did you see the World Cup… um… actually, I'm sorry…I…"
"Oh! My name's Cho. Cho Chang. I'm a fifth year. Ravenclaw, obviously."
"Nice to meet you."
The train whistle blew loudly, scaring them all a bit. They all glanced towards the clock.
"10:56! We all better get on, before we're left standing here," joked Cho.
"Er… right. Nice meeting you… Cho." They began to walk away, but when they were about fifteen feet apart, the girl spun around, shouted, "Yeah! I saw it! Great, wasn't it!"
She grinned, then they parted, each finding a separate compartment with their own respective friends.