The day a very unusual high school student picked up a notebook, the course of a detective's life changed. Though the detective didn't know this at the time.
Under normal circumstances, murder cases were run-of-the-mill. This one was never a normal case. From the very beginning it had the smell of the occult. Perhaps that should have been the first sign that things would be a constant challenge for the side of Good, even if throughout a bloody stalemate the scales tipped ever in Good's favor.
That was what made it interesting, too. The fewer the rules, the cleverer the plot. And the higher the stakes. The investigation would unfortunately claim many more lives; in fact the detective would almost certainly be killed. But this risk was more than worth it. This would prove to be a worthy exercise.
Of course it wasn't an exercise. It was real life and real people were dying. But take anything too seriously, become too attached, and it is much more likely to fail. It was best to remain distanced, an untainted observer.
Not that being the lead investigator meant that one was distanced. Just the opposite, in fact: the spearhead of the very mission, the tip of the sword, the first of the front lines was hardly untainted. But L had always taken precautions to hide that most precious commodity: identity. No, that wasn't the issue. It was emotional distance.
Luckily, that had never been terribly difficult to maintain. Perhaps that made the detective a cold human being. It was of little significance in either case. Viewing this catastrophe as a simple exercise increased the chances of success considerably. What was it that mattered in the end—the unfailing extraction of a mass murderer, or the investigative team's bedside manner?
Besides—what good was such a brain if one wouldn't make the best of it? L owed it to the world to remain detached.
That in itself would be a great sacrifice.