History Series / KamenRiderZiO

** ''Rider Time: Series/KamenRiderDecade vs. Zi-O: Decade's Death Game'' and ''Rider Time: Kamen Rider Zi-O vs. Decade: Seven Zi-Os'', set after the series and released simultaneously. While Decade and Diend were major supporting characters during the show's final arc, this is a full-fledged crossover between the two series.

* ''Kamen Rider Zi-O vs. Decade: Seven Zi-Os'' & ''Kamen Rider Decade vs. Zi-O: Decade's Death Game'', two projects announced for a February 9th, 2021 release. As the title implies, it will feature the return of Masahiro Inoue as Series/KamenRiderDecade since the original series's finale, as well as several other returning actors from previous series.

** It's used again in 11.5, to cover Tsukuyomi when she references ''Anime/{{Doraemon}}''.

* PreviouslyOn: Each episode begins with Woz giving a brief recap of the previous episode, ending with some brief foreshadowing of the events of the current episode, framed as Woz reading the events from his book.

* ''Kamen Rider Zi-O vs. Decade: Seven Zi-Os'' & ''Kamen Rider Decade vs. Zi-O: Decade's Death Game'', two projects announced for a February 9th, 2021 release. As the title implies, it will feature the return of Masahiro Inoue as Series/KamenRiderDecade since the original series's finale.

For the Showa-era equivalents, see ''[[Film/KamenRiderZX Birth of the 10th! Kamen Riders All Together!!]]'' and its manga adaptation, ''Manga/KamenRiderSpirits''. For the ''Franchise/SuperSentai'' equivalent, see ''Series/KaizokuSentaiGokaiger''.

** Every "j" sound is officially romanized as "z": Zi-O, the Ziku-Driver, the Time Mazine, the various Zikan weapons, etc. But ''not'' the Zikan Jaclaw.

* ''Kamen Rider Zi-O NEXT TIME'', a series of direct-to-video movies set after the end of the series, focusing on secondary Riders.
** ''Geiz, Majesty''

** The Time Jackers suffered from this a lot, but none worse than poor Heure, whose name is a French word that sounds odd being spoken by Japanese speakers. Previously fans thought his name was "Uhr" or even "Wool". Similarly, Ora's name was thought to be spelled "Hora" or "Aura". We only received confirmation on both when the TV Asahi website added bios for their custom Time Mazines. And we still don't know yet if the third member is "Sworz", "Swortz", "Schwartz", or something else.

* CastingGag:
** Hideya Tawada, who played the ninja-themed ''Series/ShurikenSentaiNinninger'''s SixthRanger, plays the ninja-themed Kamen Rider Shinobi. Amusingly, the two characters are complete opposites: Rentaro/Shinobi is very much the classical ninja while Kinji/Starninger wasn't, [[NinjaPirateZombieRobot to put it mildly]].
** Jingi Irie, who played Kamen Rider Kikai. He previously portrayed Jiro/Kikaider, an android-based hero in 2013 ''Series/{{Kikaider}} Reboot'' movie.

** The Zikū-Driver (Spacetime-Driver), used by both Zi-O and Geiz [[spoilers:as well as Tsukuyomi/Alpina]], is the main transformation device, while forms are changed with Ridewatches (similar to Decade's Rider Cards). Similar to the Drivers in ''Ex-Aid'', it has two slots for Watches, with one used for the personal transformation and the second for power-ups.

** The Zikū-Driver (Spacetime-Driver), used by both Zi-O and Geiz, is the main transformation device, while forms are changed with Ridewatches (similar to Decade's Rider Cards). Similar to the Drivers in ''Ex-Aid'', it has two slots for Watches, with one used for the personal transformation and the second for power-ups.

** Oma Zi-O being a version of [[TheProtagonist Sougo]] who is [[EvilOverlord Demon King]] in a BadFuture? Same thing happened before with Kotaro Minami in the {{manga}} adaptation of ''Series/KamenRiderBlack''.

** Ōma Zi-O's "Rider/ライダー" visor is vaguely shaped like a bird similar to [[Series/KamenRider Shocker]]'s symbol.

** Sougo becoming a [[EvilOverlord Demon King]] in a BadFuture? Same thing happens to Kotaro Minami in the {{manga}} adaptation of ''Series/KamenRiderBlack''.

** In ''Heisei Generations Forever'' when Tsukuyomi loses her memories, she doesn't know why someone would call her Tsukuyomi. [[spoiler:This hints that her real name isn't actually Tsukuyomi.]]
** Swartz statement to Woz that [[spoiler:he and Tsukuyomi are cut from the same cloth is revealed he was being literal; they're siblings as shown in episode 38.]]

* DarkerAndEdgier: This series opens with a very brutal BadFuture of Oma Zi-O crushing the Resistance forces and decimating them all, with Geiz and Tsukuyomi trying to guide away from being the most vile demon king. As the show progressed, Sougo has more of his FriendlessBackground emphasized with a few episodes of Geiz and Tsukuyomi staying distant from him in favor of White Woz's side, [[spoiler:the fact that Sougo and Hiryu lost their parents in a bus crash that Swartz orchestrated,]] the ''Kiva'' tribute being much more dramatic and intense than previous tributes before it, and the Another Zi-O II three-parter has Sougo suffering from a timeline change caused by Hiryu where nearly almost everyone he knows is against him. [[spoiler:Then there's also the fact that the show's final act deals with time paradoxes that lead to monsters from all over the Heisei era with the risk of breaking reality and unlike previous final battles, the climax of Sougo's involves him becoming Oma Zi-O over grief of Geiz dying to save him and then tearfully finishing Swartz after the latter also kills Tsukuyomi.]]

** The movie Riders in ''Over Quartzer'' are particularly bad, as their names are hiragana anagrams of the shows they're based off of, with no regard to how they'd work in English. "Amazons" translates cleanly to "Zamonas", while "Shin/ZO/J" only has the issue of where to stick the H, resulting in things like "Zhonjis", "Zonjhis", or "Zonjish" (or "Zonjis", if you're willing to drop it); but there is ''no'' good way to anagram "Black RX" into a seven-letter word with only one vowel. You'll see that one written as "Barx", "Burks", "BRX", "Barlux" or "Balrux", etc.; or even "Barlckx" if the writer is committed to keeping the anagram. A magazine eventually confirmed the names as Zamonas, Zonjis (no H), and Barlckxs (full anagram with an S for some reason).

** "Day Of Oma," which pays tribute to Ryuki and Blade, while dealing with the three future riders, Shinobi, Quiz, and Kikai, from Episodes 17 to 29.
** "Road To The King," which pays tribute to Agito, Hibiki, Kiva, Kabuto, and Den-O from Episodes 30 to 40.
** "New Demon King," the final arc, which pays tribute to W, the Movie Riders, and Drive from Episodes 41 to 49.

* ''Kamen Rider Zi-O: Over Quartzer'', the summer movie.

** When the cast asks Woz why Geiz's name is based on "gates" and not "gate" in Episode 2.5, he tries to make the excuse that it makes Geiz sound rich, like a millionaire; referring to the tech mogul Bill Gates.

* ''Kamen Rider Zi-O NEXT TIME'', a series of DVD movies set after the end of the series, focusing on secondary Riders.