These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: Kamen Rider Kiva
Americans Hate Tingle: In the West, Wataru is greatly disliked among the Heisei era protagonists due to his awkward, shy personality and indecisiveness. At least one of the comments to the Kamen Rider IXARe Cut stated "This is so much better without Wataru in it."
Badass Decay - When Kengo is given IXA, Nago loses a lot of his cool. And gets punched a lot.
But then he gets it back, and he spends most of the rest of the series beating the crap out of the second most powerful Fangire, Bishop- a Fangire who handed Kengo his ass on a platter.
Complete Monster - Rook. Anyone who spends every single day playing games like "let's see if I can kill X innocent people wearing Y in Z minutes" over and over again is a Complete Monster.
Though a little bit diluted by his child-like demeanor: you get the impression that he simply doesn't know any better, which makes him more pathetic than monstrous.
He ends up doing a semi- Heel Face Turn. Why? Because he has nothing better to do and wants to go to Heaven. So he does a few good deeds, then fights IXA so he can die.. Good God, Toei, of all the stupid asspulls to do...
The Rhinoceros Fangire is a better example. He tricks young people into believing he'll help make their dreams come true to lure them in so he can steal their life force. After killing them, he takes an item from them that relates to their dream as a trophey to put in his 'Dream Graveyard". His choice of prey is based solely on a love for crushing the dreams of young people and nothing else. Wataru usually tries to find the good in Fangire but he considers this guy unforgivable, that's saying something.
The original King also qualifies. He threatened to murder his own son to force his wife (who he'd told he didn't feel was worth killing because he didn't even love her) to stay away from the human she really did love and turned the last of the Wolfen, Merman, and Franken races into weapons. This guy is so evil his own loyal Transformation Trinket ultimately has enough of him and helps to kill him off.
Epileptic Trees - There were plenty, of course, but one of the most common got subverted surprisingly thoroughly. Since 1975's Kamen Rider Stronger, it's been standard operating procedure for seasons of Kamen Rider to have females who get powers to die. Since it's made clear very early on in Kiva that Yuri was going to die soon, most fans assumed that this would happen as a direct result of her getting and using the IXA powers. Come mid-season, she gets the powers, uses them in battle, kicks complete and utter enemy ass... and nothing happens. The show never really explains how she died; many fans at this point assume something relatively mild, like a car accident.
Fan Nickname: Keisuke Nago gained the nickname "753" from the Japanese fans, as their number word play reads that as "Na(na)-Go-San". This would later be referenced in the program when Nago abdicated use of the Ixa system and wore a 753 T-shirt (which you can buy too boys and girls!!).
Otoya would also receive a similar numerical nickname in one of the Net-Movies in the form of "0108" as "O-Tou-Ya" (ten rather than one-zero), but this never really caught on. Doubles as a Brick Joke as this was also part of his phone number in #5.
And thanks to all the pumping◊, the Zanvat Sword is pretty much universally known as the fapsword.
Fetish Fuel: Jiro and his silk and leather outfits, Ramon for anyone with a thing for shotas (a fandom term for his actor is "Shotabait"), Maya's ENTIRE OUTFIT, and King's outfit. A lot of the things Taiga and Wataru do in episodes are particularly suggestive (there's some serious Ho Yay and Bro Yay going on here).
Growing the Beard - The story really picked up speed after about 20 episodes, with the introduction of Mio and Maya.
Hilarious in Hindsight - ep 27 opens with Kivat saying something about time travel being a possiblility, even stating 'I'd like to return to that day'. Tomokazu Sugita would later return for the second season of Haruhi Suzumiya, infamously known for Endless Eight...
Speaking of Kivat's voice actor, one episode starts with him attempting an impression of Norio Wakamoto, referencing his role in The Movie. Sugita's dubbing of Ohja/Strike is basically the same thing. And then there's this.
Saga's finisher involves impaling and hanging fangires before ultimately causing the victim to explode in tremendous pain. One could actually feel sorry for the Horsefly Fangire for having to die in such a brutal way.
For starters, the show's basic setup (namely, the 13 Demon Races) should have allowed for a lot of interesting characters and significantly impacted what the world is like. Instead, we only really got to deal with the Fangire and The Masquerade is strong enough to ensure that next to nobody knows about the Demon Races, even when the city gets attacked by Sabbats.
What an Idiot: Yes, Bishop, do tell Taiga that you killed Mio instead of shutting up and letting Taiga continue to assume that Kiva did it, therefore getting rid of him without having to lift a finger. No wonder you are anEvil Genius!