* There were a lot of [[UnpleasableFanbase complaints]] about Tsukasa's depths of hidden knowledge, including being the first (and so far only) human to understand [[Series/KamenRiderKuuga the Grongi language]] and having extensive knowledge of the various worlds despite being an amnesiac. However, TheReveal of his identity suddenly made it all make sense: [[spoiler:as the leader of Dai-Shocker, he would have made contact with the worlds before in order to recruit races like the Grongi, and in order to study up on the biggest threats to his ambitions - the Kamen Riders.]]
** Although the InUniverse HandWave is that it's one of Tsukasa's special skills that he acquired whenever he goes to a new world, like how he could play the violin, or how he could enter the mirror world.
* An equally spoilery example is the case of [[Series/KamenRiderKiva Otoya]]'s [[WhatHappenedToTheMouse unknown fate]] at the end of the Negative World, although...[[spoiler:given the fact that he transformed into Dark Kiva a total of three times in both here and in ''Series/KamenRiderKiva'', we can see that he is as good as dead.]]
** But in that world he's most likely a kaijin, so he's probably still around.
* Why doesn't Decade have a world of his own? Well, Decade's color is Magenta/Pink, and scientifically, Magenta/Pink is not on the color spectrum - the colors Pink is a combination of, red and violet, are on the opposite sides of the color spectrum, whereas Magenta is created because of [[https://en.wikipedia.org/wiki/Magenta an absence in the color spectrum]].
* There were also complaints about the [[CurbStompBattle quick defeat]] of Great Shocker during the movie. Maybe it's ''because'' Shocker just doesn't stand a chance against an army of Kamen Riders? [[spoiler:In fact, Tsukasa, when he's still the Great Leader, seems to even try to fix this during the beginning, hence the Rider tournament.]]
* Diend being the focal character of the third movie of the ''Cho Den-O'' trilogy, where he is targetted by a TimePolice that wants to arrest him, robbing him of his freedom. Well, remember ''Diend'' world, and what's Diend's "treasure" there again? [[note]]Freedom[[/note]]
* Why did the Final Form Ride for Den-O change from the [=DenLiner=] to Momotaros? [[spoiler:Because Decade didn't ''completely'' solve the problem of ''Den-O'' world.[[note]]:a.k.a. the 4th Den-O movie[[/note]]]]
* The series as a whole is, as already mentioned, a MilestoneCelebration of 10 years of the Heisei era. Why would it go on to include the Showa era, making it add up into a '''38'''-year celebration [[note]]okay, okay, so maybe that is something for a LongRunner to brag about, but aren't celebrations reserved for multiples of 5s and/or 10s?[[/note]]? Seemingly awkward, until the Net Spinoff Videos pointed out that Decade is officially recognized as the '''25'''th Rider hero...
* Some of Diend's multi-rider summons bring forth some brilliance.
** Kabuki and Rey were [[spoiler: both good guys with dark, if [[AntiVillain somewhat good]] intentions that eventually made them side with the villains]]. [[spoiler: They might be to foreshadow Kaito's stance in the show]].
** Drake and Delta were {{The Gunslinger}}s and both names start with D. They were summoned due to them being better than G3-X's power.
** Sasword and Saga have {{Cool Sword}}s and both names start with S. Both of which have poisonous animal motifs. They were summoned to fight Den-O's ''Sword'' form.
** Ixa and Psyga are both colored white, work for an organization much like Kabuto, and at one point or another, they were bounty hunters, which is what Diend is using them for when he summons them.
** Scissors and Raia are based off sea life, ironic since they are fighting a sushi maker. Also, The two riders are from a show that the same writer from Shinkenger wrote.
** G3, Caucasus, and Ohja share the same colors as the Taros sans Momotaros.
** Punch Hopper, Raia and Gai [[spoiler: were killed by Kick Hopper and Ohja respectively.]]
*** It turns into Fridge Sorrow when you notice that [[spoiler:Kick Hopper didn't murder Punch Hopper in cold blood like Ohja. He did it as a MercyKill]].
* Having trouble determining where All Riders vs. Dai-Shocker fits in? Look near the end of #27, in which Eijiro puts up a photo. Recognize it? It's the backdrop for Decade's World, and thus, All Riders takes place between Black RX's World and Amazon's World.
* Onodera's being weaker than Godai, while frustrating, makes a lot of sense. First off, due to Tsukasa's help (or interference if you prefer) Yuusuke was force to deal with the BigBad of his world much earlier than his original counterpart did. Well before he had the opportunity to take the numerous levels in badass that Godai needed to solo the entire Grongi race. Secondly, with the Grongi defeated, and Tsukasa being pretty much alright on his own, Yuusuke probably had less motivation to fight unless it was under certain circumstances (being driven to do so, or being asked). As result he never was able to achieve the same level of strength the original Kuuga did. He could have however, had things continued in the manner they were before Decade showed up.
** Continuing on that note, Rising Ulitmate Form could have been achieved by Godai had a situation come up where he needed even more power than what Ultimate form provided (and if he hadn't broken the Arcle in the finale). After all, Kuuga is all about constantly evolving to meet the situation isn't it? Or maybe he always could upgrade Ultimate form to Rising ultimate form, but simply never got the chance (all the other forms apparently already existed) due to the events of the final battle.
* Many fans were disappointed that no EvilCounterpart for Decade ever came up, especially in Movie Wars. However, there ''was'' an EvilCounterpart in the form of the Dummy Dopant. Both start with D, and assume the forms of different people. The Dummy Dopant, along with just different people also had become a Kamen Rider and a Kaijin, thus two birds (an rider who uses evil Kamen Rides, and a rider who transforms with Kaijin Rides) with one stone.
** And WhatCouldHaveBeen indicates that there were plans for a legitimate EvilCounterpart, one that even received some {{Foreshadowing}}. Remember how in the first episode he was in Kabuto's World, he encountered a Worm that took his form? This was likely meant to foreshadow that in ''The Last Story'', [[spoiler: he would be fighting against [[EvilCounterpart Dark Decade]]. Of course, because this was ScrewedByTheNetwork, it wound up being [[DemotedToExtra Demoted To]] BigLippedAlligatorMoment, instead, but it's the thought that counts.]]
* Take a look at the episode numbers. Asides from the first episode, all the episodes are two parters, with the first part on an even number, and the second part on an odd number. Then look at the fates of the worlds in context. Nearly all of them were fine and dandy before Decade came and caused some problems, usually wrecking more things than fixing them. There are some exceptions, but for the most part, Decade comes to a world that was balanced (even) and leaves the world having changed a lot of things (odd).
* The [[ShapeshifterWeapon Final Form Rides]] may make sense only in a toyetic context at first. However, considering that the Decadriver was developed by Shocker, it may have been a way to turn a Rider into a weapon for Decade to use to defeat other Riders.
** Continuing this train of thought; the Final Form Ride system's main weakness is that you need the Rider in front of you to do it, kind of difficult when they're spread over the worlds. Ideally, you'd need a support system that can bring you the Riders you need...and what does the Diendriver do?
*** This was already addressed in Shinkenger world, where Chinomanako summons Blade to fight Tsukasa and Takeru, only for Tsukasa to turn him into Blade Blade to [[HoistByHisOwnPetard finish Chinomanako off]].
* HeartwarmingInHindsight alert: Diend Complete Form can summon movie-exclusive Riders from as many seasons as possible (but oddly skipping [[Series/KamenRiderDenO GaOh]]). One of them is Glaive...who was earlier established as Daiki's ''own brother''. Sure, he turned out to be TheStarscream to the ruler of Diend World, and looks set to take that throne for himself - [[JerkWithAHeartOfGold but that doesn't mean he'd just leave Diend hanging.]]
** Gaoh being absent actually has a very, very meta explanation. For one thing, the Gaoh suit was destroyed to make Yuuki in [[Series/KamenRiderDenO Farewell, Den-O!]], so it was impossible to bring it back. To cover this, a Gaoh Ganbaride card was released in tandem with the movie. The card is faded, like Decade's cards before being active, but is also smokey and covered in ghostly chains. The general implication of this is that, because of the events of [[Series/KamenRiderDenO I'm Born!]], Gaoh has been permanently locked out the timestream.
*** That doesn't explain why they just didn't use Yuuki instead, however.
*** Because they already had a movie-exclusive Den-O series Rider; they just happened to be fighting ''against'' him!
*** Actually, there's another reason why it makes a bit of sense why they didn't use Yuuki - all of the riders summoned by Diend Complete Form are from summer movies[[note]]Hence the reason why Ryuga was used instead of Verde, even though the latter would fit better with the other riders[[/note]] (save for Skull, although this is likely because Double's Summer movie was not out yet; had ''Episode Yellow'' come out after ''The Gaia Memories of Fate'', they would certainly have used Eternal instead). ''Farewell Den-O'' is a fall movie, and ''Climax Deka''[[note]]which has Nega Den-O[[/note]] is a spring movie. Since Gaoh's costume was used to make Yuuki's, the only other rider exclusive to I'm Born! is Mini Den-O - and since Gaoh was locked out of the timeline, there is no way that Mini Den-O could be used, and thus Den-O is not represented.
* The Queen of the Fangires has a true name, which is "''Perishing at the Altar, Silence from a Deep Kiss''", which may be gibberish, but upon careful thinking, is pretty clever: [[spoiler:Both of the Queens that the actress portrayed died just outside of an altar]].
* Tsukasa's catchphrase makes sense when you realize what he was supposed to do. "I'm just a passing-through Kamen Rider. ''Remember that''." [[spoiler: His mission was to make people remember Kamen Rider and thus save their worlds from fading into obscurity/being destroyed]].
** There's another reason too. [[spoiler: When he died, he was saved because people ''remembered'' him]]. It was a sort of Gambit to make sure [[spoiler: he lives through his mission]].
* After arriving in the Negative world, Otoya tells Tsukasa it's the world he should live in. Not only is it a paradise for him, it's also filled with monsters. Perfect for the leader of an evil organization ...
* The Nega World Riders set off some pretty heavy moments of Fridge Brilliance.
** For one, Orga is a Nega Rider. Up until him and Alternative, the Riders were flat out {{evil knockoff}}s of the heroic Riders. Then you remember that the original Orga was Kiba, Takumi's {{evil counterpart}} at worst, {{foil}} at best.
** The Alternative can also count. The system itself was an evil knockoff of Shiro's own Advent Card system cribbed off of photographic memories.
** The choices for the Nega Riders makes tons of sense considering the monsters they have and the overall theme of the world they're in, namely a world where not everything is what it appears to be. TheMovie of Ryuki (and if you count it as such, [[Series/KamenRiderDragonKnight its adaptation]]) has shown that doppelgangers exist in the MirrorWorld. Worms are able to copy human forms while Fangires assume human guises. As for Oprhnochs? They're the real person, just dead and able to turn into a zombie monster.
* The reason for Series/KamenRiderKuuga being the only one of the nine Riders getting to accompany Decade is not that random, and not some FirstInstallmentWins thing - Kuuga's suit actor was Kenji Tominaga, while Series/KamenRiderAgito was Seiji Takaiwa, who took over as the main Rider's suit actor for every season after that (sans Hibiki), so it makes sense that Kuuga and Decade are the only ones that can exist side by side!
* Gamio's version of the Ultimate Darkness seems a little ''too'' literal, but then you realize that his motif is a wolf. Werewolves are known to sire others into being Werewolves.

* Shouldn't being stuck in Clock Up mean that Kabuto is also ''aging at breakneck speed?'' Makes Final Form Ride look like a holiday in comparison...
* Speaking of the [=FFRs=], the Riders are ''[[AndIMustScream completely self-aware]]'' in their Ride forms. Does that mean that they manage to stay conscious throughout their PainfulTransformation, too?
** Adding to this, the Finale movie confirms that this can be done completely against the Rider's will, when Decade [[spoiler: turns Blade into the Blade Blade and uses him to kill the Rider Blade had been fighting alongside moments before.]] Imagine being [[AndIMustScream turned into a weapon and being used to kill one of your own allies while you're totally powerless to stop it]].
* Yuusuke's role in the Rider War [[note]]as part of the nine main Riders gunning for Decade[[/note]] might possibly mean that [[spoiler:the original ''Kuuga'' world might have already been destroyed even before the start of the series...[[note]]AU!Yuusuke probably being a substitute for OU!Yuusuke[[/note]]]]
** This is likely now not the case though, as WordOfGod states that the Heisei Riders appearing in post-Decade crossovers (e.g. Let's Go Kamen Riders, Super Hero Taisen etc.) are the originals, so Kuuga is Godai.
* Since the Decadriver and Diendriver [[spoiler:were created for use by Dai-Shocker]], many an unsavory theory was bound to crop up regarding the Riders' [[OneWingedAngel Final Form Rides]].
** Another unsavory theory comes when you realize that [[spoiler:the original 9 Riders were banking on Tsukasa, the leader of Daishocker, to ''kill'' them]].
* Thanks to the EarlyBirdCameo from Double, we know that, while Decade is unable to beat Shadow Moon, Double is able to defeat him with ease, but struggles when facing foes like the Luna Dopant, which had to be taken out by OOO... who struggled with Gara until Fourze helped... who, with Meteor, had a hard time defeating all twelve Horoscopes at the same time before Wizard stopped by... Who, along with the thirteen other Riders, couldn't beat Amadum until Gaim stepped in and beat him easily...\\
Worse still... Remember how Gaim took out Amadum? The Energy Riders are stronger than him ''and'' the other Armored Riders sans Zangetsu (who promoted himself to Energy Rider). So, if one is to actually look at the power scale without invoking PowerCreepPowerSeep, the Energy Riders are essentially stronger Amadums ''in Rider form'' and could easily destroy the other Riders. And keep in mind, the Energy Riders are the ''villains'' in Gaim. We're lucky their goals have nothing to do with conquering places and instead are all focused on one small town, otherwise they would have easily won.\\
So, in short, Tsukasa's lucky he didn't travel to the Worlds of OOO, Fourze or Wizard, or that he didn't encounter even a single Dopant or Inves or had to fight against the Armored Riders and Energy Riders (whom he teamed up with) when he traveled to Futo and Zawame City in ''Film/HeiseiRiderVsShowaRiderKamenRiderWarsFeaturingSuperSentai'', since the inhabitants of those worlds might be able to curbstomp him. The World of Drive might be safe ground though, since Drive is the first Rider since Decade himself to not get involved in an EarlyBirdCameo with his immediate predecessor.
** Except the part involving Wizard gets negated if you read the fridge page on the entry for ''Series/KamenRiderWizard'': Gaim was able to beat Amadum because, in Amadum's eyes, Gaim didn't exist yet; like [[Series/KaizokuSentaiGokaiger Basco]] struggling against the [[Series/TokumeiSentaiGobusters Go-Busters]] when the latter made their EarlyBirdCameo, Amadum couldn't foresee someone he didn't know existed interfering (and by the same token, you could also say that about any of the other monsters that were defeated by riders making an EarlyBirdCameo) - odds are that if Haruto had summoned Drive, Ghost, or Ex-Aid instead of Gaim, they would have faired just as well against Amadum. Not to mention, odds are that if Decade went to the world of Gaim/Wizard/Fourze/OOO, he would probably gain Gaim's/Wizard's/Fourze's/OOO's cards - and in Gaim's case, he'd gain access to the Kachidoki Arms and the Jimber Arms form cards, which have been shown to be able to stand against the New Generation Riders. And before you try and point out that Decade didn't have OOO's/Fourze's/Wizard's cards in Kamen Rider Taisen, that's because he wasn't visiting an AR World of Zawame City - he had visited AR Worlds of all the riders he had cards for.
** Double's appearance in ''Movie War Megamax'' negates this even further - by the same logic, Double should have barely been able to defeat a single Zodiart. Yet he was able to effortlessly defeat 4 of them. Considering that Decade has proven that he's capable of handling Double's world, I'd say that he has nothing to fear from the other worlds. Really, Tsukasa should really consider himself lucky that he didn't visit the world of GARO instead.
* Tsukasa got a young kid to commit regicide ''and'' patricide. (In Kiva's World)