Hermes Trismegistus, also known as Mercurius ter Maximus, also known as Hermes the Thrice Greatest, is a syncretic deity in the Roman Empire, a mixture of the Greek god Hermes and the Egyptian god Thoth. Explains why the Sisters have Greek names, but outfits with a Middle Eastern flavor, as well as the design of the malgams based on Egyptian sacrophages. Also, according to Cicero, there were 5 Hermes/Mercuries and I would venture to guess that the other 4 will also appear in the show. A possible option is a summer movie, as in Build, or the guards of the main boss, as in Saber.

Fuga is Houtarou's dad? Houtarou and Rinne are twins separated at birth like Luke and Leia? That'd be a very bad twist. If it's true, then the use of memory loss/memory manipulation trope in this story is solely for the sake of shock factor, aka throwing "Gotcha!" moments at the viewers.

Another possibility that I forgot to mention is that Nijigon/Chemy #101 could be a (re)fusion of all 100 Chemies. This logic works similar to KR Agito, where the duality of the Overlord of Light and the Overlord of Darkness shows that they're basically two different sides of the same entity. If the uber-demon/Chemy #0 represents the force of destruction, then the original form of Nijigon/Chemy #101 represents the force of creation. Chemy #0 and #101 are basically the manifestation of the dual nature of power as the force of destruction and creation.

Like the Overlord of Light who spread its power inside humans at the beginning of the universe and later manifests as the Agitos, the light/positive side of Chemy #0 was divided into the several primordial Chemies like Dragonalos and Gaiard (and probably also several other Cosmic and Fantastic Chemies) during the creation of this world, and then later about 120 years ago the majority of the remaining Chemies were born in a brief period of time, probably by the help of the Alchemist of Dawn who pioneered new techniques and advanced the progression of the alchemy world. So, basically Chemy #101 is the original form of the fusion of Chemies #1-#100.

I've read the production notes of episode 27 here and found no mention of the name Hermes nor Hermes Trismegistus. The only mention of the name Hermes Trismegistus is in the production notes of episode 8 here, where it mentioned that Hermes Trismegistus was the father of alchemy that was associated with the number 3, thus inspired the ubiquitous use of triangles and arrows as the main motif in Gotchard's various designs and iconographics. The article didn't explicitly state that the name of the uber-demon that was defeated by the Alchemist of Dawn 120 years ago was Hermes nor Hermes Trismegistus.

Like stated by Mesnick above, Hermes Trismegistus is the mythical father of alchemy who is a syncretic, mythical figure based on Greek and Epyptian deities. So, the article might imply that the ubiquitous use of triangles/arrows (a symbol which was commonly associated with Hermes Trismegistus) means that the use of alchemy is basically tapping into a very tiny portion of the uber-demon's powers (and or its positive counterpart's powers like I mentioned in my hypothesis in the previous comment above). The uber-demon's name may be revealed later as Hermes, Hermes Trismegistus, or something else, but as for now, the producers and writers of this show have never officially revealed it. Hermes Trismegistus could've even been the name/title of the Alchemy of Dawn as the founder/original member of the Alchemys Union, as the triangle/arrow motif is omnipresent in the AU's logos, symbols, etc, including Houtarou's and the other Riders' transformation pose, barring KR Dread.

The only sources that mention the uber-demon's name as Hermes or Hermes Trismegistus are a page on TV Trope and several other articles/Reddit threads/tweets by fans/fansites. It was probably started by a hypothesis made by someone on Twitter, Reddit, or other forums, and several other people picked it up and posted it on TV Trope, which inspired another batch of people to repeat the same hypothesis and report it as theory/fact. So, I conclude that it's very likely a positive feedback loop of misinformation. It's a common occurrence in this age of social media.

Several other people hypothesized that the uber-demon's name was El Dorado as muttered by Glion at the end of episode 27, although it could've been a reference to his twisted obsession of creating a golden world, basically making the El Dorado myth come true.

Also, I think that since Gotchard as a show really loves the number three, we have three Chemies Dragons for a reason. I think we'll see three dragon riders at some point in this show.

Wouldn't be the first time KR did a secret family reveal, after Kabuto, Den-O, Kiva, Double, Ghost and Geats. After playing Romeo and Juliet though, it might be a little weird to try that between Houtarou and Rinne at this point. Either way, I think memory loss for lazy plot twists is still better than memory loss as a lazy plot twist, looking at you Revice.

The problem with this theory is that all 101 Ride Chemy Cards were already seen with Fuuga in Episode 1. If what Dragonalos Malgam said is true, then I'm inclined to believe that Nijigon is the youngest Chemy, perhaps born from the collective powers of the others, or otherwise enhanced by them. So, like your theory, but inverted. And since we know that Fuuga can create doppelgangers of himself to pilot remotely, then it's possible for him and Nijigon to be in the same place at the same time even if they're the same being. Maybe Houtarou needs to create #102 to have the strongest Gotcha-N-Go with Nijigon.

Okay, I stand corrected. When misinformation is repeated often enough like this, it becomes a factoid and it would seem that I have fallen in to that trap of believing Hermes was canon. In the absence of a true name though, I think it does suit him based on the etymology. But now I'm hearing about Dark King Gigist, which sounds like it's derived from the Trimegistus part, so maybe it wasn't that far from the truth.

The 3 main Riders are basically 3-in-1 alchemists, there are 3 Dark Sisters, Geryon's golden cube is 3^3, Houtarou and Rinne have advanced to Class 3-A and 3 dragon Chemies coming soon. If we get a new insert song after What's Your Fire, then that will be the third. Maybe the final boss will add a 4 instead, just to be ominous.

https://i.imgur.com/eN9jPx1.jpg
There were 101 RCC's with Fuga in the second scene of episode 1, but several of them were partially obscured, including #101, probably because the artworks weren't finished, haha. Like what I posted here, Nijigon has at least 3 cards, 2 of which very likely exist simultaneously, so the RCC #101 that appeared in that scene could've been Nijigon's egg/default card.

Anyway, I'm worried about the direction of this story when I realized that the mooks appearing in the preview for the next episode were the Kasshines aka the Hundred's mooks from KR Legend spin-off, so the next episode could be the start of the new arc that features KR Legend who could also debut in the same episode or episode 33. This king of darkness guy Gigist may be a villain from KR Legend's world who crossed over to Houtarou's world to mess up the storyline, haha.

And maybe the next episode will be the debut of the 3rd OP to mark the start of the new arc? Haha.

I also thought that Revice was the prime example of the laziest of the laziest of the laziest, the cheapest of the cheapest of the cheapest, the shallowest of the shallowest of the shallowest of plot twists. ...Until this putrid, hideous, monstrous abomination came along.
https://i.imgur.com/b4o10XD.jpg
Kamen Rider Geats should be rightly called Kamen Rider Gotcha for constantly barraging viewers with lazy, cheap, shallow "Gotcha!" moments in virtually every single episode. Another story screwed up by an out-of-nowhere memory manipulation powers to create a lazy, cheap, shallow "Gotcha!" moment is The High School Heroes (2021), where the story went FUBAR in the last 2 episodes, especially in the last one. It's no wonder because those episodes were written by *drum roll* *drum roll* *drum roll* *wait for it* the great, mighty God of asspull: Yuuya Takahashi.

This is why stories that abuse the memory loss or memory manipulation trope make me cringe, especially the memory manipulation one. That trope is often used as the easiest, the most convenient tools to create lazy, cheap, shallow plot twists and an infinite number of asspulls. Two other tropes often used as asspull and shock factor generators are reality manipulation trope and multiverse trope. These 3 tropes are often abused by hack writers to create a false image of excitement and narrative grandeur. At this point I'm 95% sure that if a story features a memory or reality manipulation trope, then it will throw at least one lazy, cheap, shallow plot twist at me, like in Gotchard's story where it was revealed that Glion was the one who manipulated the AU's top brasses' memories, or like in (God forbid) Geats. Sigh... So, this is the so-called "modern writing".

Speaking of this episode, TTFC released a special, which is a recording of the play "Romeo and Juliet" also in the mockumentary style. Considering this, We are Class 3G, Kamen Rider Legend and Hyper Body Swap Battle, Gotchard can safely be called the craziest show in terms of its specials. There was something slightly similar in Zi-O, but even there there was no such variety and flight of fancy.

Rinne manages to overcome the torment from Atropos with the help of Minato, though it?s the cliche reason for her realizing she has friends by her side albeit it?s something fitting for her due to her previously struggling to socialize.

Both girls finally open up about their feelings of jealousy towards each other. Seina shares her backstory of being heroically saved by Houtaro and given a new direction in life, while Rinne simply claims that Seina is unbeatable. The theory is that Seina's ability to socialize and blend in easily is the source of Rinne's jealousy. Rinne possesses many other advantages compared to the ordinary Seina though, as she excels in everything except socializing.

This is demonstrated when she seamlessly steps into Juliet's role due to her thorough knowledge of the lines. Her acting potential is further recognized by Seina when Rinne convincingly feigns defeat against the Malgam that caught him off-guard. This makes Seina acknowledge the deep trust that Houtaro and Rinne have for each other.

As the typical secondary Riders, she got to be the cool one that is shilled by almost all characters (at least there?s Houtaro, Supana, Renge, and now Seina). It is ironic that Rinne's triumphant moment through acting is contrasted by the opinion of some fans who find her acting wooden.