Disclaimer: Naruto is the intellectual property of Masashi Kishimoto and various other parties. The Harry Potter series is the intellectual property of JK Rowling; various publishers including but not limited to Bloomsbury Books, Scholastic Books, and Raincoast Books; and Warner Bros., Inc. No money is being made from this story, and no copyright or trademark infringement is intended.

Author's Note: This was a slightly belated birthday gift for Asuka Kureru, who asked for a crack Naruto/HP crossover. I don't know how I did on the crack factor, but I did manage the crossover part. Sort of.

"An Ounce of Prevention" will not affect canon in either series -- that is, it takes place during the Naruto timeskip and before Harry Potter and the Chamber of Secrets. All characters and props will end up in the right places and conditions for Naruto's return to Konoha and the Weasleys' trip to Diagon Alley in 1992.

Summary: During the timeskip, Sakura finds a very interesting diary among Tsunade's books and papers.

Chapter 1: An Ounce of Prevention

Sakura examined the strange book she'd found in Tsunade's file room earlier that afternoon, turning it over in her hands. She'd been looking for an obscure medical text on the use of insects to treat infections, and the thin, shabby book had fallen off the top shelf and hit her shoulder.

It seemed to be a diary, but its previous owner hadn't written anything but his name. He had odd handwriting -- the strokes of his characters were thin and angular, as if he'd been writing with an overly stiff brush.

Maybe he'd used a quill or one of the pens that were becoming popular for quick notes, Sakura concluded. She ran her hand along the diary's spine and flipped the pages in a cascade, enjoying the rustle of paper.

"Hanjimono Tomu," she said, reading the brief inscription on the inside cover. It was a nice name. Tomu, to become rich -- perhaps his mother had dreamed of a bright future and named her son with her hopes. Hanjimono, a puzzle, an enigma -- the diary certainly was a puzzle. She wondered why Tomu hadn't used it. She wondered how it had ended up in Tsunade's hands. A gift for her services as a healer? Gambling winnings? Tsunade never won anything normal or easily converted into cash, after all.

In any case, Sakura had thought for a while now that it might be useful to keep a record of her studies under Tsunade, to organize her thoughts and make notes of things she wanted to research further -- things that might let her help Naruto search for Sasuke, or help Sasuke recover once they brought him home. There was so much to learn, and so little time.

She might as well use Tomu's diary for her notes. It would be a shame for such a well-made book to remain empty.

She opened the diary, inked her brush, and began. "Today Tsunade-sensei asked me what medic-nin should do if they are injured in ways that block their ability to manipulate chakra, or are caught in seals that--"

Sakura hurled the diary across the room, drew a kunai, and set her hands in the dispelling seal. "Kai!"

Nothing changed. The diary lay inert on her floor, halfway between the dresser and her closet.

Nonetheless, Sakura approached it warily. Normal diaries did not absorb ink as if they were drinking.

Thin, angular characters welled up through the page: --Hello? Is anyone there?--

"Yes," Sakura said.

The diary did not seem to have heard. Words continued seeping onto the page, even as the first lines sank back into the depths of the book. --Hello? Please write to me; I'm trapped in this diary, and I can only read what you write in its pages. I haven't talked to anyone for years. My name is Hanjimono Tomu. Who are you? Will you tell me your name?--

That was out of the question; no ninja would give her name to an unknown, potentially dangerous person or creature. However, it would be wasteful to destroy the diary before learning what jutsu had been used to create it. And perhaps this entity claiming to be Hanjimono Tomu was the soul of a person who'd been trapped by a seal. If so, it was Sakura's responsibility to learn the technique and inform Tsunade, who could then decide whether or not to declare it forbidden... and whether or not to release the person it trapped.

Nothing said that Tomu had been trapped unfairly, after all.

Sakura laid the diary back on her desk and inked her brush. "Hello, Tomu. My friends call me Hana."


AN: Thanks for reading, and please review! I am, as always, particularly interested in knowing what parts of the story worked for you, what parts didn't, and why.

To clear up potential confusion, yes, Hanjimono Tomu is Tom Riddle. I translated and transliterated his name into Japanese because it amused me, and was subsequently forced to think of a semi-logical in-story explanation. (Translation spells are my friends. +grin+)

ETA: This chapter was edited on 7/5/08, to make the beginning of the story match thematically with the ending. The plot has not been affected.