* CashCowFranchise: ''Den-O'' has been living on well beyond the year-long expectancy of its fellow ''Rider'' series, and doesn't look to be dying anytime soon. Lampshaded in the opening Imagin skit in ''Farewell, Den-O''.
-->''"Well, for all the talk of 'Last' and 'Farewell', it's always common practice to make a sequel, isn't it?"''
* TheCastShowoff: Takeru Satoh portrays 1 character who's gained a total of 7 different possessed personalities (some of them by force), sings in every version of Double-Action (except Gaoh Form, Coffee Form, Climax Form, and Strike Form), his own solo song, Real-Action, and, thanks to Ryutaros, has an excuse to demonstrate his breakdancing skills.
* FanNickname: Thanks to the Egyptian-looking collar and other elements, Shiro is sometimes called ''Kamen Rider Phara-Oh''.
** Because of his skull and crossbones mask and resemblance to Gaoh, he's also sometimes known as Gaoh Pirate Form.
* HeyItsThatGuy
** Most obviously, Yuto is played by Yuichi Nakamura, who was Kyosuke Kiriya in ''Series/KamenRiderHibiki''.
*** Todoroki appears as a ninja squad leader in the first movie.
** Naomi is portrayed by Rina Akiyama, who also played Mana Kazaya in ''Series/KamenRiderAgito''.
** Suzuki, the detective who helps the team in ''Climax Deka'', is played by Ryota Murai, who would go on to play [[Series/KamenRiderKuuga Yusuke Onodera/Kuuga]] in ''Series/KamenRiderDecade''. Additionally, his father is [[Series/KamenRiderBlade Hajime Aikawa/Chalice]].
** Kazuki Namioka, the Imagin contractor from episodes 3-4 went on to portray Demon Knight in ''Series/GenSeiShinJustiriser'', Shishimaru/Lion Maru in ''Series/LionMaruG'', and Lock Dealer Sid in ''Series/KamenRiderGaim''
** Yumi Saito, one of the Imagin contractors in episode 7-8, is played by Hitomi Kurihara who is also the BunnyEarsLawyer in ''Series/KamenRiderRyuki'', also the Smart Lady from ''Series/KamenRiderFaiz''.
** Saizo from the first movie is Shuichi Tadokoro from ''Series/KamenRiderKabuto''.
** Miku Uehara, the Imagin contractor from ''Chou Den-O Trilogy: Episode Blue'', was played by Yuko Takayama, who [[RetroactiveRecognition went on to become]] [[Series/KamenRiderWizard Rinko Daimon]].
* HeyItsThatVoice
** Momo/Ura/Kin/Ryu = [[Anime/MobileSuitGundamWing Duo Maxwell]]/[[Manga/{{Bleach}} Gin Ichimaru]]/[[Manga/{{Naruto}} Hidan]]/[[Manga/DGrayMan Lavi]], and Deneb sounds kinda like [[Manga/{{Naruto}} Jiraiya.]] For bonus coincidence points, note that Momo's voice, Creator/ToshihikoSeki, also did the Japanese dubbing for ([[Creator/DavidTennant the tenth incarnation]] of) [[Series/DoctorWho a certain Time Lord...]]
** Koji Yusa, Urataros' seiyu also voices [[VideoGame/SonicTheHedgehog Shadow the Hedgehog.]]
** Sieg is voiced by Creator/ShinichiroMiki.
** Corrolary to the aforementioned Masaki Terasoma connection regarding Kintaros, this guy also voiced [[Series/KamenRiderBlack Shadow Moon]][[note]]And as an additional bonus, Kintaros's suit actor, Jiro Okamoto, did the suit role for Black![[/note]].
** Kohana is [[Anime/CodeGeass Empress Tianzi]].
** Negataros is voiced by Creator/HikaruMidorikawa.
** The Cobra Imagin from ''Ore, Tanjou!'' is played by Takashi Hagino, AKA [[Series/KamenRiderRyuki Takeshi Asakura/Kamen Rider Ohja]]; as an ActorAllusion, the Imagin's costume was designed with more than a few similarities to Ohja's.
* {{Irony}}: The premise of the ''Cho Den-O'' trilogy: the films shine the spotlight on Zeronos, New Den-O and Diend, shoving Den-O ''himself'' in a [[OutOfFocus supporting role]] instead. (Fans did complain about ''Den-O'' becoming a CashCowFranchise, after all...)
* PropRecycling: The movie Riders use reworked Den-O suits; taking it a step further, Gaoh's suit was used to create Yuki, which is the reason [[Series/KamenRiderDecade Diend Complete Form]] doesn't have a Den-O representative[[note]]The producers wanted to use Gaoh, but couldn't because they didn't have the suit anymore, so they decided to just leave Den-O unrepresented.[[/note]]
** The {{Mooks}} in ''Onigashima Warship'' are Gelnewts from ''Series/KamenRiderRyuki''; in an amusing crossover with RealLifeWritesThePlot, ''Detail of Heroes'' explains that this is entirely because the makers of ''Series/KamenRiderDragonKnight'' ordered Gelnewt costumes in bulk to use as the Mook in ''their'' series.
** A few of the Imagin were reworked from others; for example, the Owl Imagin from Ryutaros' character focus episodes was turned into the Bluebird Imagin that appears late in the series. More obvious examples include the Leo and Albinoleo Imagin (both of whom are Kai's subordinates) and their Leo Soldiers (reworked from [[Series/KamenRiderKabuto ZECTroopers]]).
* RomanceOnTheSet: Takeru Sato (Ryotaro) and Rina Akiyama (Naomi) dated for a while in 2008.
* StarMakingRole: Of all the ''Kamen Rider'' main actors, Takeru Satoh is the actor with the most abundant post-''Rider'' career.
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