Every single episode of Kamen Rider Ex-Aid and nearly all of its movies were penned by head writer Yuya Takahashi alone with no additional writers helping him, though some did write a few specials that he supervised. Previously, the only made-for-TV Kamen Rider season to have been written entirely by its head writer without others was Kamen Rider Faiz (not counting the Amazon Prime series Kamen Rider Amazons, which also has every episode written by the head writernote Ironically, the only installment she didn't write, the Grand Finale movie, is instead written by Yuya Takahashi under her supervision).
Inverted with Ren Amagasaki/Lovelica Bugster. Shinya Kote plays Ren in his human form, while Junichi Suwabe voices him in his Bugster form. Suwabe's voice is dubbed over Kote's performance when Ren is using his Bugster abilities in human form.
Also played with with Emu and Parado. Hiroki Iijima plays a Parado-possessed Emu, and Shouma Kai voices (temporarily) Ex-Aid Level XX R.
Actor Allusion: More of a singer allusion, but the Hyper Muteki Gashat jingle performed by Hironobu Kageyama could easily pass for a GARO theme. Also one of its major lines is "Sparking!" One of the closing lines of the first opening of Dragon Ball Z, CHA LA HEAD CHA LA, is "Sparking!" and it was also sung by Kageyama.
The Jet Combat Gashat announcement references Kageyama's performance of the Choujin Sentai Jetman opening theme.
Kageyama put so much into just a couple days of recording that he blew out his voice for a bit.
Casting Gag: Tetsuya Iwanaga, who plays Kuroto Dan, is actually a licensed pharmacist in real life. Ironically, the character he plays is one of the few main characters who is not a doctor, even if he did create the Rider systems. Yet, like the character he plays, he is a genius. Iwanaga is a member of the Japanese branch of Mensa and was once given a rating of Triple-A for the astronaut aptitude test from JAXA. In an interview, he also said studying is his hobby and has acquired a number of licenses and qualifications. So, there's also a case of Reality Subtext here.
The Cast Show Off: Hiroyuki Takami who plays Masamune Dan/Kamen Rider Cronus, is also the singer for the legendary Japanese band, ACCESS. In the series, he sings WISH IN THE DARK, showing off his vocal chops. Later, he also sings JUSTICE, his own character's image song.
Cowboy BeBop at His Computer: This Anime News Network article about the debut of Poppy as a Kamen Rider initially called her the first female Kamen Rider even though there's been multiple female riders a fewtimesbefore. Fortunately, they corrected the article not too long after posting it to clarify that Poppy is the first female rider with her own exclusive transformation device. At least until Cronus debuts, since he uses the same device. Even then, she doesn't count as such, because Natsumi Hikari is the first female Rider with a unique device and with Cronus' debut, still holds that unique distinction. Yes, she relies on a Kivat like Kiva and his variants, but unlike the latter ones, she doesn't use a belt, just the little bat herself as a trinket, not unlike a Magical Girl's trinket. Although if one was to exclude movie-exclusive riders, which Natsumi falls in the category of, then Poppy would have held that distinction until the debut of Chronus.
Dawson Casting: Inverted. As revealed in the Ex-Aid character book, Taiga is 29 years old, making him the oldest of the four main heroic riders in Ex-Aid. However, in an inverse of this trope, his actor is currently 21 years old. It's the same with the other actors. Kiriya is 27 years old, while the actor playing him is currently 23 years old. Emu and Hiiro, who are both 24, are played by actors who are 20 and 21, respectively. There is also an aversion with Kuroto, whose age is the same as his actor, which is 30 years old.
Defictionalization: Mighty Action X was released as a legitimate 3DS game to promote this series. It can be downloaded through a code after purchasing All Kamen Rider: Rider Revolution, provided you have a Japanese Nintendo eShop account (and a Japanese 3DS to boot).
Lots of people immediately jumped to the conclusion that Ren was the Bugster from Tokimeki Crisis after he used his reprogramming powers on Poppy.
There were plenty of fans who thought Parado was actually part of Emu as an Enemy Without.
Many fans managed to guess that Masamune Dan was Kamen Rider Cronus and would be the true villain.
The fact that Kuroto will be revived later, because a mad programmer like that must have some kind of contingency plan, and the actor doesn't receive flowers after being seemingly killed on episode 23.
Since Kiriya was revived without any brainwashing on his part and his whisper to Emu before he was punched was never heard, many fans guessed that Kiriya hasn't turned evil at all and was letting Emu in on a secret plan.
As 2017 is the fifteenth anniversary of Kamen Rider Ryuki, Takeshi Asakura/Kamen Rider Ouja returned in a special starring Hiiro/Brave, portrayed by his original actor. Furthermore, in Chou Super Hero Taisen, Shuichi Kitaoka/Kamen Rider Zolda will also return as one of the main protagonists alongside later heroes. Not to mention Parado's Level 99 transformation pose is similar to Ryuki's pose when he's about to execute his Final Vent.
Similarly, it's the tenth anniversary of Kamen Rider Den-O, hence why the Imagin gang are back in the Chou Super Hero Taisen movie.
One Steve Limit: Averted in a meta-sense, both of the actors playing Parado and Graphite have the same first name, Shouma.
Hiroki Iijima/Emu Hōjō and Toshiki Seto/Hiiro Kagami are fans of Kamen Rider Ryuki, to the point that their favorite riders are Shinji Kido/Ryuki and Takeshi Asakura/Ouja respectively. Seto would even costar with Asakura in Kamen Rider Brave: ~Lets Survive! The Revived Beast Rider Squad~.
Shōma Kai/Parado is a massive fanboy for Kamen Rider Kuuga, which he made abundantly clear in most of his answers during a post-Ex-Aid cast interview.
Recycled Script: Not exactly same, just similar. In Kamen Rider OOO there was an episode with a genius surgeon held back by her father, the director of the hospital she worked at. She was banned from performing operations on anyone and was justifiably angry, which made her a perfect piece in Kazari's next plan. The reason was that her father didn't want her to become surgeon with all the skills, but no compassion and responsibility as he put it.
Enter Hiiro, another genius surgeon, who treats patients as procedures and has little respect for anyone, who does otherwise. Also, he avoids taking responsibility for risky operations. In his case, it's Taiga, who brings this up. Ironically enough, Hiiro's father indeed is a hospital director, but too much of a absent minded weirdo to thought anything like this.
When Seiji Takaiwa was filming his scenes in the Ex-Aid Level 2 suit, he ad-libbed the blowing into your cartridge trick thing before performing the Rider Kick. That being said, the film crew were actually damn cool with it and allowed him to continue doing it indefinitely.
As detailed on the Funny page, Kurotos characterization as an Evil Is Hammy maniac with a god complex is the result of his actor ad-libbing a particularly crazed Evil Laugh in one scene and them rolling with it.
Trolling Creator: Toei seems to enjoy trolling Kiriya fans after his death, ranging from releasing a t-shirt depicting his death and causing a massive uproar on Twitter.
Reportedly, Break The Darkness by Rider Chips was intended to be the insert song for either Maximum Mighty X or the Kamen Rider Chronicle arc. However, it was pushed aside in favor of People Game, and was eventually used for a Pachinko Machine of Kamen Rider BLACK. Interestingly enough, this led to Maximum Mighty X being left without an insert song despite the series having them, much like Agito's Burning form.