Similarities Between Kamen Rider Kiva and Danny Phantom
While I'm about to wrap up Kamen Rider Kiva vs. Danny Phantom, I do think Danny Phantom was an inspiration to Kamen Rider Kiva in some way aside from previous Kamen Riders like Black (the two fighting to succeed the previous king) and Kuuga (supernatural monsters that threaten humanity) but it seems to be Toshiki Inoue had taken some elements from Danny Phantom as well.
Both Wataru Kurenai and Danny Fenton are heroes who fight the supernatural. In the case of Wataru, he was born between a human and a Fangire which wasn't revealed until later that he was half-Fangire. Danny got his powers thanks to some molecular rearrangement that made him part-human, part ghost. Both are born from idiotic fathers- Wataru's dad Otoya is a moron and Danny's father Jack is also a moron. Wataru is however an only child of his father (he and Taiga have different fathers), allergic to the world for some stupid reason while Danny is more outgoing and has one full sister in Jazz.
Megumi Aso and Sam Manson- They are both the females who fight supernatural enemies in their continuities while never actually killing much less defeating them. They are also close friends to the protagonists though Megumi and Wataru didn't become a couple nor were hinted, unlike Danny and Sam who are somewhat hinted. Both also have hot-headed mothers though Megumi's mom has long died.
Kengo and Tucker appear to be close friends with the hero and have their own falling away. However Kengo for me is Tucker Foley gone wrong.
Both Otoya Kurenai and Jack Fenton are pretty much idiotic fathers who sired heroic sons. In the case of Otoya Kurenai, he has long passed into the afterlife by the time his child has become a late teen.
The Wonderful Blue Sky Organization is apparently similar to that of the ghost hunting agency in Danny Phantom except with much more personality differences between its members.
Taiga Nobori and Dash both have their love interests who love the hero. In Dash's case, Paulina only loves Danny Phantom not Danny Fenton, in the case of Taiga, his lady love Mio loves his maternal half-brother Wataru which like their late fathers, history repeats itself. But Taiga exists as a villain who reforms eventually.
Mio Suzuki and Paulina Sanchez are the love interests of the heroes, both I never liked. Paulina is in love with Danny Fenton's alter ego as Danny Phantom, Mio likes Wataru 100%.
Both Bishop Fangire and Vlad Masters are expert schemers, cunning and manipulative existing as recurring antagonists. In the case of Bishop Fangire, he seeks to revive the true King of Fangires while Vlad Masters has other plans of his own as the big bad.
Rook Fangire and Skullkur both play their own deadly hunting game in their own ways.
The Fangire King and the King of Ghosts rule their respective realms that are basically a threat to human existence. However the Fangire King had a MUCH BIGGER role than the King of Ghosts who was shelved out in favor for Vlad. Both of them are extremely menacing and powerful.