The curtains were drawn around Ginny Weasley's four-poster bed in Gryffindor tower. She lay on her side, propped up on one elbow, and had a quill in her hand that was delicately balanced over an inkwell. Ginny hesitated just a moment before plunging it in and beginning to write in a blank book, pausing only after completing a paragraph. She didn't seem at all startled when the book began to write back.
"You keep writing about Harry Potter," it wrote, and the young girl began to blush. "What is it that you like about him so much?"
She paused again, considering his question, before beginning to write. "It's not the scar. I'm certain it's not the scar in itself at least. But it's not the fame, either. I mean, sure, that's why I know about him. I grew up hearing story after story of the Boy Who Lived and how wonderful he was. So, maybe my mum's stories have something to do with it. It's not that he's particularly attractive, either, or that he's Gryffindor or my brother's best friend. It's just, I guess, that one thing about him that makes me so tongue-tied around him I can't speak."
"That one thing?" The diary asks, and Ginny can tell it- he- is confused.
"See, that's the thing, Tom. I'm not even sure. He's kind, charming, funny, and not affected by his fame the way Professor Lockhart is. And when he smiles at me, my heart starts beating extra fast and I can't breathe normally and I can't manage to say two words to him." Even by herself in her dorm room, Ginny was embarrassed to write those things down. How childlike of her, really, to have a crush on her brother's best friend. How typical. "Oh, Tom, I'm sorry I keep telling you all of this."
"Don't worry. I find it all fascinating. And..." The page that moments ago was covered in her own and Tom's handwriting was suddenly blank again. "I can keep a secret," it finished, beginning again at the top of the page.
Ginny smiled despite herself. "I think that might be what I like best about you. Even if I lose this book or forget it somewhere, or give it to someone else later on, they will never be able to tell what it was I wrote in here."
"But you don't plan on giving this book away, do you?" The speed of his writing had significantly quickened. "After all, I am the only one you can trust. I'm the only friend you've made at this school, aren't I?"
She sighed. "Well, yes, you are. I don't want to get rid of you, anyway! It is wonderful to have someone who really cares about what I'm saying. I love having you for a friend."
"Good. I understand that friends do each other favors?"
"Of course!"
"Then do as I say." The next thing Ginny remembered, she was in Moaning Myrtle's bathroom washing the blood off her hands.
A/N: I'm still not JKR and the characters and situation belong to her. This was for the Taragh Word Limit Competition, and my prompt was 'that one thing' and the word limit was 500. Different word counters have this between 500 and 530 words, not counting this author's note.