Disclaimer: Just so everybody knows, i do not own code geass or its trademarks, and i do not own deathnote or its trademarks.
If Lelouch had a Deathnote: How Code Geass would have happened.
Lelouch rushed home. He had found the answer to all his problems. It was there, laying on the staircase, beckoning him. Enthralled, he found himself reaching out and picking it up. It was a plain notebook, all black, with the words Death Note scratched into the cover. Flipping through it, he found it empty. Blank. However, when he reached the back, there was a set of instructions on how to use the notebook. A crazed look came over Lelouch's face. He knew how to get back at Britania and his father.
Now he was sitting at his desk, the light casting an eerie shadow across his room. He flipped the cover open to the first blank page. A page of opportunities. Now, to test it. And he knew the perfect target. Prince Clovis, viceroy of area eleven. He dramatically reached for the pencil, freshly sharpened for the deed. With a flourish, he wrote the name: Clovis La Britania. He cackled meniachally as he put down the pencil shut the book.
The next morning, it was formally announced that Prince Clovis was found dead of a heart attack. There's more where that came from, Lelouch thought.