1) By not taking on the Kira case
This one is pretty self-explanatory. If L had never taken on the case, he never would have made it onto Light’s radar as an enemy. L’s name and face weren’t known to the public in any form, and he was too smart to have committed a crime that would end with his face on the news. So, he definitely could have survived Kira’s rule that way.
2) Always wear a mask
I don’t know if any of you remember a fantasy manga called Fushigi Yuugi, but there was a character named Chichiri who always wore a mask. And it didn’t get in the way of him breathing, speaking, eating, seeing, or anything really. Plus, he always carried back up masks in case something happened. Well, not even the Shinigami Eyes could get the name of someone through a mask. So, L should have taken a page out of Chichiri’s book. After all, if a mask like that existed in ancient China, it should exist in modern day Japan.
3) Become a better liar
In the battle of wits between Light and L, Light was definitely the better liar. That’s one of the big reasons he won. So, L just needed to get better at lying than Light. This leads to the question, why was Light so much better at lying? Easy- he had lots more practice, because he was a lot more sociable. Unfortunately for L, this would’ve meant he needed to go out and talk to people. Not as L, the detective, but as a random dude with a name NOT stolen from a famous celebrity. With enough practice, L could have honed his lying skills to rival Light’s. Then, maybe, he could’ve outwitted the teenager.
4) Joined Kira’s side
Another pretty easy one. Light was after L because L was trying to stop his “justice”. So, if L had decided to fight for Kira’s cause instead of against it, Light never would have needed to kill him. Imagine how crazy it would have been if L had gone through all that trouble to find Kira, and in the end been all, “Actually, I was looking for you because I want to join you.” That utopia probably would’ve lasted longer than six years.
5) Let Misa go and keep Light locked up forever
Light was the mastermind anyway, so L could just let an amnesiac Misa go. Then, with Watari’s help, he could escape to England or whereever with Light and keep him locked up forever. Send fake love notes from Light to Misa for a few months before breaking up with her. And voila! The killings stop because Light’s locked up and Misa’s doesn’t remember ever being the second Kira. Rem has no reason to tell Misa about the Death Note again, because she’ll be relatively safe and happy. Not to mention, Higuchi wasn’t nearly as careful or as smart as Light. So, L would have caught him eventually anyway.
By his own admission, L had lots of criminal contacts. And by his own actions, he obviously had no issue using them. Since he had a thief and a con artist in his back pocket, why not an assassin too? And if not, it couldn’t have been too hard for him to find one. And once he was absolutely sure Light was the culprit, he just had to put out the hit. Granted, this would have meant that the series was over in like a quarter of the time, but still. Light assassinated. Kira stopped. L alive.
7) Gotten bored
L only ever took cases he was interested in. If he had gotten bored with the Kira case, he could have abandoned it easily enough. And with L no longer chasing him, why should Light bother trying to kill him? After all, Light only ever killed criminals and the people who tried to get in his way.
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