Disclaimer: I do not own any part of Death Note, its characters, or its story line. I am merely a fan who wishes to add a personal twist to the story.
Author's Note: This story takes place primarily in the second half of the Death Note storyline, the part where Near is fighting Kira. However, the prologue takes place prior to L's death, so that is the point in which the facts of the story begin to change. This story is based off the manga, not the anime or the live action movies.
Vaccine
Prologue
A few days before Rem's death…
Watari was always a man of efficiency and secrecy. He could hack into almost any database in the world when given the right reason. It therefore was to be expected that Watari's computer security system was without peer, an impenetrable fortress against the outside world. So why, Watari wondered as he was sifting through files, was there a video file stuck into the notes on the Death Note on his hard drive when no one had been given access to the files besides himself and L. And why was the video file labeled 'urgent message' when Watari and L had numerous ways of contacting each other without resorting to hidden messages like this. Where had the file come from?
After checking the file numerous times for hidden viruses, Watari finally decided to open it. As the video started playing, a black and white YinYang symbol came up on the screen. Across the image was the word 'Vaccine' in a soothing blue color. A woman's voice, unaltered by any audio editing software, started speaking. "Greetings, Watari and L. I am Okashira Tamiko. I give you my real name as a sign of good faith, but my face I shall keep hidden a little longer, though you could no doubt find it if you tried. I send you this message as a gift, a show that I am not interested in any sort of power for myself other than being able to counter the works of Kira before he can strike. I know you have in your possession the Death Note that belonged to Kyosuke Higuchi, and therefore understand the rules and restrictions bound to the book. However, one thing the book does not mention, nor should it, is that there is a way to become immune to its power. This is what I offer you: a vaccine against the disease that is the Death Note. In return, though, I need your help…"