Ragnarok (fanfic)

Ragnarok by Skeptikitten is a Death Note AU Slash Fic in which a Serial Killer emerges in Japan basing his murders on Norse Mythology. NPA star-detective Light Yagami and the World's Greatest Detective L are both targets, and the case may lead to the end of the world for both of them.

Tropes used in Ragnarok (fanfic) include:

Alternate Universe Fic
Ambiguous Disorder: L and Near.
Ambiguously Evil: Mikami stalks Light and is an overall creep but it's yet unclear if he's actually villainous or not.
And Your Little Dog, Too: when L takes Light into protective custody Loki targets Light’s friends and family.
Annoying Younger Sibling: Sayu to Light.
Arrogant Judo Guy: Light.
Awesomeness By Analysis: This is Light, L, and the Wammy's kids forte.
Big Bad: Loki
Big Brother Instinct: Light to Sayu.
Black and White Insanity: Light as a teenager. His father caught on to this and intervened, retraining him to think of the world in shades of grey.
Boxed Crook: "Kira" is a hacker that works for the NPA to avoid prison time...
Broken Ace: Light. Fortunately for Light his father noticed his growing mental problems and intervened. Later Aizawa notices that it's not just his enormous ego but that the rookie Light is feeling the pressure and feels he needs to be perfect all the time.
Buddy Cop Show: Light and Matsuda are partners on the force. Also Light and L.
Calling Card: The Nordic runes
Camp Gay: Mello
Celibate Hero: Light hasn't been in a relationship with anyone for over a year nor felt the need to have one.
Chaste Hero: L just doesn't get the whole relationship thing. Once when he was 16, and curious about why people make a big deal about sex, he had Watari procure for him the services of a couple of prostitutes. He never tried again.
Co-Dragons: Fenrir, Jormangandr, and Hel to Loki.
Crazy Jealous Guy: Mikami to Light and L to Light
Criminal Mind Games: Loki challenges L with taunting messages and even names a future target—Light Yagami.
Dark and Troubled Past: Light realizes he nearly went insane as a teenager and was a "future Serial Killer in the making."
Detective Drama
Eureka Moment: Light has one when L and Mello are bickering.
Even the Guys Want Him: Light
Face Palm: when Sayu meets Light's "new friends" while insulting all of them:

Light sighed again, pressing the heels of his hands to his eyes. That migraine was assured now- damn all little sisters to the blackest pits of hell.

Fish Out of Water: L sends Mello and Matt to spy on Light. Since they are in the middle of Tokyo, Light notices the blonde kid spying on him almost immediately.
Fix Fic: There is no Death Note so Light isn't as crazy as he is in canon. Also the author says it's not going to be a Kill'Em All ending like in canon however it's not going to be an Everyone Lives ending either.
Funny Foreigner: Mello is making fun of Light and Japanese stereotypes while showing off his own very British mannerisms.
Genius' Sweet Tooth: L and Mello of course.
Get a Room: Matt suggests this to L and Light when they are in the middle of some very emotionally-charged bickering.
Grey and Gray Morality: Souichiro teaches Light to view the world this way.
Hero Worshipper: Light towards L. Also Misa towards Light.
Hollywood Hacking: Matt and Light.
Honey Trap: L orders Light to use Mikami's infatuation with him in order to further the investigation... and then gets angry and jealous when it works.
I Know Karate: Light knows Judo and L of course knows Capoeira.
If You Ever Do Anything To Hurt Him:

Misa: Hello, Mr. Great Detective! Play nice with Raito-kun; he's a genius but a bit difficult. Oh, and if anything happens to Raito while he is under L's care, Misa-Misa will destroy him if it is the last thing she does!

I'm Standing Right Here: When Light and L begin speaking of Mello like he's a highly contagious disease while he's in the room with them.
Insufferable Genius: Light and L
It's Personal: Loki seems to have a personal vendetta against L and Light; blaming them for his imprisonment.
Leaning on the Fourth Wall: when building a profile for "Loki" it's mentioned that mangaka often use Norse Mythology in manga and anime.
Love Dodecahedron: Mello and Matt are in a relationship but Mello still engages in some uncomfortable flirting with Light and Mello and Matt make it clear they’re open to a three-way. Light dated Takada in college, had a brief but happy affair with Stephen Loud a.k.a. Gevanni of the FBI, and he went on a single date with Mikami before realizing how crazy he was and has been trying to avoid him ever since. Misa loves Light but they agree that they're Better as Friends. L has been stalking Light for the past year and Light has been stalking L. Also Near gets all flustered around Gevanni and Sayu.
Murder, Inc.: Loki's crew.
Must Have Caffeine: Light as L Must Have Sugar.
Mythology Gag: L sets up his new headquarters at the Yellowbox Warehouse.
National Stereotypes: Lampshaded and mocked when Mello is being his politically incorrect self.
Nerd Glasses: Light wears these occasionally, like when reading for hours through the ancient tomes for clues.
The Nicknamer: Aizawa nicknames Light as "Bocchan" or "young master" in reference to his enormous ego.
Norse Mythology: Naturally this is "Loki's" theme.
Not Good with Rejection: Takada and Mikami.
Not So Different: Light knows he nearly went insane as a teenager and was a "future Serial Killer in the making."
Not That Kind Of Partner: Matsuda is Light's partner on the force. Mello asks if he's his partner in every sense of the word.
Odd Friendship: Misa and Matsuda are Light's closest friends. Later Light with L and the Wammy's kids-especially Near. Also Sayu and Mello.
Online Alias: The hacker variety. Matt is Red13 and Light is Kira.
Only Known by Their Nickname: Loki and his minions.
Overprotective Dad: Souichiro Yagami.
Pastimes Prove Personality: L plays the piano and Light took singing lessons. L quips that Light must like hearing the sound of his own voice. Also Matt and Light bond over hacking.
Platonic Life Partners: Light and Misa
Playful Hacker: Matt and Light
Plug N Play Friends: Lampshaded on how well Light gets on with the Wammy’s kids.
Politically Incorrect Hero: Mello
The Profiler: L and Light
Properly Paranoid: Light and L.
Religious and Mythological Theme Naming: Loki and his crew. Also in his taunting notes Loki refers to the Taskforce as Asgard, L as Odin, Mello and Matt as Huginn and Muninn, and Light as Balder.
Reluctant Psycho: Light. Fortunately his father caught onto this early enough to retrain him out of his Black and White Insanity to follow a different moral code. He still struggles with this and has to constantly remind himself "Shades of gray, Light. The world exists in shades of gray."
The Rival: Light and L
Rules Lawyer:

Light: Technically, Kira is Matsuda's source, not mine. I have never stated that I was not, in fact, Kira. Technicality is the soul of the law.

Shout-Out: L plays Strange Currencies on the piano.
Slash Fic: L x Light and Matt x Mello are the main pairings.
Sleep Cute: Light and L.
The Sociopath: Light worries he would have become one had his father not caught on to his growing disgust with the world and intervened. Light still worries he might become one seeing as mental illness may have genetic as well as environmental components.
Sophisticated As Hell:

Light: So the gist of all these deaths is that the stars have fallen, the fate of the gods- the law - is set, and I'm fucked. Gods, this guy is a douche.
L (laughing): I do not expect that officers of the law usually use such terms to refer to their quarry, Light-kun. Perhaps Mello is a poor influence on you?

Stalker with a Crush: Mikami to Light, L to Light and Light to L.
Super OCD: Light
Tabloid Melodrama: to Light's dismay the tabloids become interested in the pretty boy cop that Misa hangs out with and write up a trashy article about him which concludes that if he and Misa aren't a couple then he must be gay.
Theme Serial Killer: Loki and his minions.
Too Clever by Half: Light, lampshaded by Aizawa.
Transparent Closet: Light
Tsundere: Sayu
Unconventional Formatting: Matt's lines of code. He complains that Light is wasting time being neat when the router doesn't care. Light retorts that he often has to show his work to the NPA and this way it's easier to catch if you make a mistake.
Vomiting Cop: Light, to his great embarrassment, upon seeing a particularly grisly crime scene.
X Meets Y: Death Note meets CSI and Criminal Minds.
Yandere: Takada. When Light began dating her in college they agreed it would be nothing serious since they both wanted to focus on their careers. But when Light broke up with her Takada did not take it well and has held a grudge for four years and seems to be out to ruin Light's career.