Zero vs. Kira

Zero vs Kira by Crossover Maniac is a Code Geass and Death Note crossover where Light Yagami is teleported to the Code Geass world when a Britannian world-breaching experiment Goes Horribly Right. Furious that the Britannians tried to kill him and enslaved his country, Light introduces the power of Kira to the Code Geass world when he declares war on Britannia. Also seeing no immediate way of returning home feels he may as well create the New World he envisions here. Meanwhile, Kira's activities have put a Spanner in the Works for resident Magnificent Bastard Lelouch's plans and as Zero he intends to do everything in his power to bring Kira down...

"Ryuk: killed herself. Light: Oh."
 * Affably Evil: Light is apparently "the best roommate a guy could have!"
 * Alternate Universe Fic
 * Another Dimension
 * Arbitrary Skepticism: "There's no such things as curses or the supernatural! That’s completely ridicu--" *ick, gack!*
 * Arch Enemy: Light and Lelouch.
 * Arson, Murder, and Admiration: Lelouch is admittedly jealous that Kira has accomplished what he set out to do.
 * Asshole Victim: The Brittanian soldiers.
 * Badass: Light and Lelouch.
 * Badass Bookworm: Light and Lelouch.
 * Bad Guys Do the Dirty Work:
 * Butterfly of Doom: Inverted, many positive changes have been happening to Lelouch and his world since Light's arrival...
 * Butt Monkey: Light has usurped Lelouch in this role as well...
 * Casual Danger Dialog: "What took you so long?"
 * Classified Information: Which is easily accessed via geass command or supernatural notebook.
 * Colliding Criminal Conspiracies: Kira's presence has really screwed up Zero's plans.
 * Contrived Coincidence: somehow a porthole Rem opened and a porthole the Britannian military opened connected, sending Light to the Code Geass world.
 * Crazy Prepared: Light and Lelouch
 * Crazy Survivalist: Light.
 * Curb Stomp Battle:
 * Dead Fic: Unfortunately. This fic hasn't been updated in a little less than two years.
 * Dead Person Impersonation: Light.
 * Deadly Decadent Court
 * Death by Racism: Colonel Taurus
 * Death Seeker: Suzaku, more so after
 * Did We Just Have Tea with Cthulhu?:
 * Do Not Adjust Your Set: Light sends a message to the media informing everyone that if the Brittanian forces don't leave Japan Kira will kill the royal family.
 * Driven to Suicide:
 * Due to the Dead: This trope gets invoked when both the Britannians and the Black Knights are LOOKING REALLY HARD (cutting up corpses) to find the cause of the mysterious heart attacks.
 * Dying Like Animals: Bats, lambs, sheep, lemmings, ostriches, mules, foxes, chimeras...
 * The Empire
 * Evil Versus Evil: Kira versus Britannia
 * Faking the Dead: When Light kills the royal family he misses Lelouch and Nunnally because they are listed as dead.
 * Fate Worse Than Death:
 * Fish Out of Temporal Water: Light, Lampshaded by Tarou "Sometimes, you act like you've been living in another world or something."
 * Fix Fic: for Code Geass Light's presence creates a ripple effect preventing a certain Deus Angst Machina from ever coming to pass...
 * For Science!
 * Full-Circle Revolution: In chapter 6, Zero holds a press conference telling Kira that he has simply "substitute(d) the tyranny of the Britannian Empire with your own."
 * It does settle an years-old arguement: Lelouch is morally superior to Light because he truly believes "Only those who are willing to be killed should be allowed to kill", while Light just kills whoever annoys him.
 * In addition, the Black Knights come to the conclusion that, ultimately, Kira's "justice" is draconian, does not allow the Japanese people to judge their own in a fair trial, and may even extend to death for the least serious of crimes. Even Kallen, who was originally a staunch supporter of Kira, changes her view when she realizes that her own mother, whose only crime was drug abuse, is at risk of being killed by Kira.
 * Gambit Pileup
 * General Failure: Colonel Taurus and
 * Gone Horribly Right
 * The Good, the Bad, and The Evil: you decide which is which.
 * Gray and Gray Morality
 * Hollywood Hacking
 * Horrible Judge of Character: Tarou.
 * I Have a Family
 * I Know Your True Name
 * I Lied: it's what Light does.
 * Intercontinuity Crossover
 * It's All About Me
 * Kick the Morality Pet
 * Kick the Son of a Bitch
 * Lack of Empathy: Lampshaded

"C.C.: No, I never made a contract with anyone named "Kira"... I don't know anyone by that name, and I don't know anyone with an instant death Geass, either."
 * Last Request: "Could you at least tell me your name?"
 * Mad Scientist
 * Magic A Is Magic A: Lelouch and C.C. are puzzled because they had attributed Kira's powers to Geass but they don't seem to be following the rules...
 * Magic Versus Science
 * The Magic Versus Technology War
 * Man Behind the Man:
 * Morality Pet: Tarou, Light's roommate (he was in desperate need of one... My God, it's the future. My parents. My co-workers. My girlfriend. I'll never see any of them again... (Beat) Wohoo!)
 * Mugging the Monster: "Damn uppity Eleven, you think you're somebody because you can speak English and wear a suit."
 * The Multiverse
 * Not Me This Time:

""I HEARD THE FIRST TIME! NOW SHUT YOUR TRAP AND LEAVE ME ALONE!" Lelouch shouted in annoyance of Nunnally's persistence."
 * Not So Different: Lampshaded and defied.
 * The Only One Allowed to Defeat You:
 * Our Wormholes Are Different
 * Out-Gambitted
 * Out of Character:

"Ryuk: The Shinigami in the last dimension I was looking in chased me around with swords. They even called me names. I don't know why they called me 'hollow', but I didn't like it."
 * WAAH! SUZAKU IS MY ENEMY SO I WILL BE AN ANGRY Emo TODAY AND TAKE IT OUT ON PEOPLE I LIKE!!!
 * Patriotic Fervor: Light is very upset that his country is enslaved in this universe.
 * Portal Network: the Shinigami Realm functions as one.
 * Red Shirt:  but that wasn't much of a spoiler, was it?
 * Roaring Rampage of Revenge
 * Say My Name: "Ki...rrrraaaa"
 * Shadow Dictator: Kira.
 * Shout-Out


 * Spanner in the Works: Light to Lelouch's "tasks at hand" by  Later Lelouch to Light's plans
 * The Spook: Kira
 * Succession Crisis
 * Swirly Energy Thingy
 * They Would Cut You Up: When the Brittanian soldiers are beating up Light the scientist cautions that they don't be too rough with him... because he wants to dissect him.
 * Too Dumb to Live: Emperor Charles declines an offer of immortality even after a mysterious force has threatened his life...
 * Colonel Taurus, full stop.
 * Transplant: Light and Ryuk in the Code Geass world.
 * Trapped in Another World: Light. Ryuk comes to keep him company.
 * Unexpected Successor:
 * Unwitting Pawn: Lelouch and is he ever PISSED when he finds out.
 * Versus Title
 * Villainous Breakdown
 * Villainous Demotivator: Britannia
 * Wham! Episode:
 * Xanatos Gambit: When Lelouch and Light go at it, its only a question of when.
 * You Owe Me Apples
 * You Remind Me of L: "Looks like your fighting L all over again. Hyuk hyuk."
 * You Will Be Spared: subverted, HARD!
 * Zeppelins from Another World: Or rather "Giant Mecha From Another World"
 * Zeppelins from Another World: Or rather "Giant Mecha From Another World"