* 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.
* {{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, although one does have to wonder why they didn't just use Nega Den-O instead, considering that they used Ryuga instead of Verde to represent ''Ryuki''[[/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.
** Speaking of ''Onigashima'', the suits worn by the main villains, Kuchihiko and Mimihiko, are modified versions of the suits worn by [[Film/KamenRiderTheFirst Reboot! Kamen Rider Nigo]] and [[Film/KamenRiderTheNext Reboot! Kamen Rider V3]].
** 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.
* WhatCouldHaveBeen: Promotional materials for ''The Onigashima Battleship'' showed Ryutaros-possessed [[Series/KamenRiderRyuki Ouja]] wielding [[Series/KamenRiderAgito G3-X]]'s GX-05 Cerberus Gatling Gun, presumably loaned to him by an Urataros-possessed G3-X. However, in the movie, R-Ouja only wields the Ryuvolver. One possible reason for this change is that in the movie, Diend ends up summoning G3 instead of G3-X, and plans to have R-Ouja use the GX-05 were scrapped due to G3 not having access to the GX-05, as U-G3 is never seen using any of G3's weaponry. Alternatively, it could be that G3 was the rider that Diend was intended to summon all along, and the GX-05 was included in the promotional material by accident.
** As hard as it might be to believe, ''Final Countdown'' '''WAS''' originally intended to be the end of ''Den-O''. However, then along came the Chou Den-O films...and the rest is history. It was the last movie Takeru Satoh was contracted to do for Den-O, hence the reason why Takuya Mizoguchi plays Ryotaro in every one of the Chou Den-O movies and the ''[[Series/KamenRiderDecade World of Den-O]]'', as it would have been too expensive to rehire Satoh by that point.
* YouLookFamiliar: If Naomi reminds you of someone from another Heisei Kamen Rider Series, it's because her actress, Rina Akiyama, previously played Mana Kazaya from the first Kamen Rider series Yasuko Kobayashi wrote an episode for, ''Series/KamenRiderAgito''. Coincidentally enough, the next role she would play would be in a work by ''Agito'''s writer, Toshiki Inoue[[note]]in case you're curious, said work was a cameo as a police woman in the summer movie for ''Series/KamenRiderKiva''[[/note]].
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