Rosario to Kiva

"No matter how many times I see it happen, it is always cool."

—Mizore Shirayuki, referring to Kiva's Emperor Form

A masterpiece from the minds of Kamen Rider Chrome and Ten-Faced Paladin, creators of such fics like Showa X Vampire, Love Hina Double Trouble, and Kamen Rider OOO: The Medals of Ikki Tousen. A crossover with Kamen Rider Kiva and Rosario + Vampire, Rosario to Kiva is one of the most popular of fanfics. It was published on October 6th, 2008.

A teenage Wataru Kurenai enters Yokai Academy in an attempt to escape his crapsack life. He soon encounters the super-cute vampire Moka Akashiya, who takes a quick liking to both him and his blood. He soon creates more friends and foes as the secrets of his heritage are slowly revealed to him- secrets that his harem may very well be connected to.

Tropes used in Rosario to Kiva include:

Anti-Hero: While he was still trying to kill Kiva, Saga wasn't evil to begin with. The proof is in the fact that he saved Kurumu from an incubus and Mizore from a Mind Flayer.
Adorkable: Wataru tends to be shy, reticent, and easily flustered around girls. All of that just makes him more attractive to them, particularly once they experience his compassionate nature.
Arranged Marriage: A forced type is attempted on Taiga and Mizore. It does not go through. Later played straight with Tagia and Mio. Unlike the canon though, they have found real romance in each other.
Balanced Harem: Because Wataru is a prince, he can marry all the girls in his harem. The only question that remains is if they are willing to share.
- They are, so now the question is: Who's first wife?
Battle Couple: With Inner Moka, though it's quite a while before they admit their feelings for each other. Still, they admit it a lot sooner than Tsukune and Moka do in the canon manga or anime. It is eventually upgraded to a Battle Harem.
The Berserker: When his Fangire blood is forcibly awakened by Bishop of the Checkmate Four, Wataru descends into this trope, attacking anyone and everyone in his path no matter if they're friend or foe.
Beware the Nice Ones: Wataru may be the nicest dhampir ever, but do not mess with people he cares about. You will not end well. At all.
- Do not betray Mizore's trust. You will regret it.
Big Damn Heroes: Wataru, like any good superhero, is fond of doing this.
Break the Haughty: When Moka's younger sister Kokoa comes on the scene, she thinks very little of Wataru and resents him for getting between her and her "real" big sister, the inner Moka. Kurenai takes over, thrashes her one-on-one as Emperor Kiva, and even gives her a spanking to top things off. This somewhat backfires, as Kokoa ends up adoring Kiva just like she adores Inner Moka... and feels the same way toward Wataru as she does with Outer Moka.
- Happens to the Inner Moka after her first defeat against Rook. She was really pissed about being beaten so easily and was steaming about it for a while.
Cain and Abel: Wataru has this with his half-brother Taiga, King of the Checkmate Four, who considers humans lower than dirt and is also attracted to Moka. Of course, Wataru manages to turn things around and Taiga soon becomes an ally.
Christmas Episode
Chrome Champion: In Emperor Form, Kiva acquires golden armor with a matching cape, and in quite a glittery shade, too.
Clueless Chick Magnet: Wataru doesn't quite understand what is so particularly appealing about him. The girls around him are more than willing to explain (heh, heh, heh).
Cool Sword: The Garulu Blade, which enables Wataru to transform into a werewolf-based form with increased speed, agility, and reflexes. In Emperor Form, he acquires the Zanvat Sword, which is initially an Evil Weapon controlling him before Wataru's willpower --- with some help from the Arms Monsters --- wins out over it.
Covert Pervert: Mio, appearently.
Did You Just Have Sex?: Both Kurumu and Gin are able to tell that Moka and Wataru had sex and confront them respectfully.
Dhampir: Wataru is a Fandiri, which is the Fangire equivalent of this trope since Fangire are technically a subset of vampires that has gone on a divergent evolutionary path.
Dropped a Bridge on Him: Shiramine was left behind during the battle against the Legendorga clan. What happened to him after is unknown. Not that Mizore cares. Not after what he did.
Fantastic Racism: Bishop's deep hatred for Wataru. He often referse to him as "that bastard half-breed".
Forgotten Childhood Friend: Remember the little boy Mizore accidently scared away when she was little? That was Shiramine, A.K.A. Kamen Rider Rey. Although he did miss Mizore and regreted breaking Mizore's heart, he saw Wataru as an obstacle that must be removed. Bishiop took noticed and made him into his mole. Needless to say, Mizore did NOT take that kindly.
Goofy Print Underwear: Wataru's red boxers have bats on them.
Harem Hero: Wataru is Type 2.
Heel Face Turn: Taiga and Rey-Kivat.
Hot Shounen Mom: Maya, who, thanks to Ruby's magic, looks exacly the same way she did in the year 1988. And then there's Tsurara Shirayuki, Ageha Kurono, Fujiko Sendo. Can't forget them.
"I Know You're in There Somewhere" Fight: Moka does this with Wataru on a few occasions, most notably when he's transformed into the Emperor Bat and when Bishop has forced his Fangire blood to the surface to make him an unthinking berserker. Thanks to The Power of Love, it always works.
Insult Backfire: The Mummy Legendorga does this, countering the Inner Moka's catchphrase:

"(Know) my place? Girl, I am one of the mighty Legendorga Clan! The most illustrious of all the Mazoku! You are a mere vampire! I know my place quite well! You at my feet bowing like the inferior you are!"

Love Triangle: Wataru/Moka/Taiga before Taiga meets Mio.
- In 1988, its Ageha/Otoya/Tsurara. Sadly, this is what cause the two women to be broken up.
Love You and Everybody: Despite his reservations, Wataru can't bring himself to hurt any of the girls in his harem by choosing one over the others, such is the depth of his feelings for all of them. Thus, they go with the Tenchi Solution.
Magnetic Hero: For a guy who's so shy, especially around the opposite sex, he sure attracts a lot of girls... and ends up making many of them into friends and even more, despite the nature of their initial encounters.
Marked Change: Wataru's Fangire markings tend to manifest when he's ready to transform into Kiva and really wipe the floor with some troublemakers.
Nice Guy: Wataru. "Kurenai" is where Beware the Nice Ones comes into play, but even Wataru himself is not someone you want to push... or else his own righteous fury might just sync perfectly with Kurenai's natural aggression.
Power Glows: When first transforming into Emperor Form.
Perfectly Arranged Marriage: Taiga met Mio in one of his classes. They became close friends even before it was revealed that she was Queen.
Rescue Romance: How Wataru ends up winning over many, if not most, of the girls in his harem.
Rule of Three: Two Words: Hat Trick.
Secret Legacy: Wataru is the inheritor of the power of Kiva, the birthright of the Fangire King.
Sibling Team: With Taiga/Kamen Rider Saga, after Taiga's Heel Face Turn.
Sixth Ranger: Mizore/Kamen Rider Lady Rey and Kokoa/Kamen Rider Kivaraa
Spear Counterpart: "Kurenai" to the Inner Moka.
Super-Powered Evil Side: Subverted. "Kurenai" is a secondary personality that represents the aggression and bloodlust inherent to Wataru's Fangire side, but he is the farthest thing from evil, just much bolder and more assertive than Wataru tends to be. You could say that he's the male counterpart of the Inner Moka.
Upgrade Artifact: The Garulu Blade has the same effect on Inner Moka as it does on Kiva, granting her heightened speed and reflexes. We have yet to see what happens when she uses Kiva's other weapons.
Teenage Spinoff: Wataru is sixteen in the story while he was twenty-one in the canon.
Tenchi Solution: Wataru is presently navigating through this with Moka, Kurumu, Mizore, and Ruby. (Yukari is exempted for the time being because of her age.)
They Wasted a Perfectly Good Plot: The "Den-O and Kiva" chapter.
- Chrome announced that Fairy Tale would not make an appearance here. Note that a lot of people were disapponted as they hoped to see a Kahlua or Akuha Shuzen VS Saga battle. Let's hope this happens anyway.
Wham! Line: A lot.
- "That's my mother. I have a portrait of her in my home."
- "Was your father named Otoya Kurenai?"
- "You're lucky that Akasha-chan taught me about her seals in case my sons would need them."
- "I hope you're alright... My Queen."
Yamato Nadeshiko: Mizore nearly becomes a permanent one due to the influence of a Mind Flayer. Saga quickly fixed that.
Yaoi Fangirl: Both Kokoa and Mio. Though Kokoa is a much more vocal about it.