Touma is an author and a Kamen Rider, so he's using both a pen and a sword, as a play on the quote "Pen and sword, in accord."
The actual Japanese wordplay used for Saber's concept is Bungou × Kengounote Literary Master × Sword Master, due to both terms using the same kanji "Gounote 豪", which means master, signifying he is a master of both the pen and the sword.
In English, the words rider and writer can be pronounced very similar to one another, saying each word without emphasizing the d and the t respectively produces this result. Thus Touma can in turn be referred to as a Kamen Writer.
The Megid refers to Tel Megiddo, which is believed to be the site of the biblical Armageddon; and The Bible is a religious book made of many books, like theone that was split up to become the Wonder Ride books!
This carries over to the name of the first episode: In The Beginning, There Was a Flame Swordsman.
Saikou's finisher is also called Hikari Are, Japanese for "let there be light".
The reason why there are three types of Wonder Ride Books (Sacred Beasts, Animals, and Fictional Stories) is because they represent actual genres in real books. Sacred Beasts represent books about mythology, Animals represent encyclopedias about many types of wild creatures, and Fictional Stories represent books about fairy tales and legends.
By rotating the letters 90-degrees left, the runes, as (pre-stylized) English text, can be read top-down, then right-left, just like traditional Japanese.
Another moment of brilliance comes from the spines of certain books in the Northern Base: since those would normally be written with the top part of the letters facing the front cover, when they are converted to "Wonder Runes" the title of the book will be upright.
Among the Legend Rider Books and where they get divided in the three categories make sense for the following:
Legendary Creatures:
Agito: Not only is he dragon-themed, his forms are also elemental based plus the Unknown are angelic-based monsters serving the will of the OverLord, a godlike being.
Ryuki: Like Agito, also dragon-themed, but also is a fire-elemental and a knight whose majority of his fights are in an alternate dimension.
Faiz: Despite being technology-based, the Rider's main user, Takumi, is also the Wolf Orphnoch, and the fact that he became one in a fire accident could liken him to being somewhat of a werewolf.
Hibiki: Is an Oni and the Makamou he fights are carnivorous demons.
Wizard: As with Agito and Ryuki, he is also dragon-themed, plus he is a magician, meaning he has magical abilities and elemental powers, and fights Phantoms, mythology-based demons that are born from people in deep despair.
Gaim: Not only is he based on a samurai, his series deals with the godlike power of the Forbidden Fruit and other mythical aspects such as Yggdrasill, DJ Sagara being a serpent, and four of the Inves being based on China's Four Symbols.
Ghost: He is basically... a ghost, plus some of the luminaries in his series are those with clandestine techniques such as Musashi or Nobunaga.
Animals:
Kuuga: He is not only based on a stag beetle, but Gouram also has a stag beetle mode.
Blade: Apart from his rhinoceros beetle motif, the Rouse Cards he and his fellow Riders are mostly animal-themed (except for two), which are the sealed states of the Undead they fight.
Kabuto: He and his fellow Riders are based on various terrestrial invertebrates, with their Zecters acting as swarming bugs themselves.
Kiva: One of the themes he has includes a bat, greatly attributed by the fact that he transforms using his partner Kivat, as well as his Garulu Form being werewolf-themed that has him fighting savagely.
OOO: Animals are his main theme, being able to use Combos that have a common animal theme.
Build: Not only are he and most of his fellow Riders animal-themed, animals make up the majority of the biotic Fullbottles.
Zero-One: He, his forms, and his fellow Riders are all animal-themed, most conveying animalistic characteristics in battle.
Stories:
Den-O: The Imagin (the Taros included) are all based on fairytales, much like the Wonder Ride Books.
Decade: His main aspects is travelling in his journeys, which includes changing the A.R. Worlds he visits in some way, basically like making or altering an existing story; plus his main weapon is the Ride Booker, and including his camera profession, both reference photo books.
Double: Phillip often researches keywords Shotaro gives him in the Gaia Library, which is full of books and information, not unlike Fantastic Bookstore Kamiyama.
Fourze: One of his 40 Astroswitches includes the Pen Switch, which activates the calligraphy brush-looking Pen Module on his right leg, somewhat symbolizing the fact that Touma is a writer/author.
Drive: The Roidmude investigations reference mystery and thriller genres in books.
Ex-Aid: All games tell a story whether in the game itself or through supplementary materials.
Zi-O: Woz often refers to events of his series through the Ohma Advent Calendar, which is like a large storybook.
Fairy Tale Wonder Ride Books are the only ones that can be non-elementals as they do not display the face of any specific Rider to be assigned to
Touma believes books are for everyone because he is a writer and that is the only way a writer could make money and reading is one of the basic rights every human should get.
Why does every Rider in the series thus far have a sword-based name? It's logical given that their organization is the Sword of Logos, and thus the Rider designations would probably be themed code names (e.g. Kaenken Rekka's wielder would be Saber, Suiseiken Nagare's wielder would be Blades, and so on).
Slash's transformation involves the words Get a gun! I would rather go with a Sword. Sword is the weapon of Hanselnuts to Gretel WRB and Gun is the weapon of Bremen No Rock Band. Tetsuo appears to be ashamed of how his personality changes when using Bremen No Rock Band, so he would preffer to stick with Hanselnuts to Gretel.
Why is one of the attacks called Learning Flash? Because the swordsman is teaching someone a lesson by hitting them with it.
The position of the initial Wonder Ride Books of the Seiken Swordriver users all allude to their character and position of their story:
Touma's is in the first slot to showcase that he is just starting as a Kamen Rider.
Rintaro's is in the second slot to showcase his status as an experienced in the middle of his journey.
Kento's is in the third or rather last slot since he knows the end of Touma's childhood and foreshadowed the possible end of his story in Chapter 13 where he disappears into darkness.
The "real world" as we know it being an Alternate Universe actually sheds some lights on certain elements.
The fact that aside from those directly involved no one else seemed to be aware of the incident 15 years ago.
The Sword of Logos so readily turning on Touma makes a lot of sense when you consider the circumstances.
Touma went after Calibur and came back reciting his creed… just like Daichi himself. Ryo and Daishinji are thus trying to avoid another Calibur situation.
Ren had a Big Brother Worship towards Kento, so the fact that Touma has started agreeing with his killer would not sit well with him.
Rintaro has devoted his life to the Sword of Logos as a family, so the idea of a traitor within its ranks would naturally leave him wanting to keep his family secure by removing the traitor.
Befitting the show's book theme, that would explain why there are more Story Wonder Ride Books than Legendary Creatures or Animals, especially since some have names based on existing tales (ex: Peter Fantasista).
Possibilities for why Rintaro is the only Northern Base Rider who transforms with an Animal-type Wonder Ride Book as well as there being somewhat lesser Animal books than Stories or Legendary Creatures: there was already Zero-One right before it, which had animal motifs among its Riders and forms; plus some of the Story-type books have some animal connotations to them, like Saiyuu Journey and Kobuta 3 Kyoudai.
Also, the dragon inside of it has been dead for hundreds of years and has nothing left but bones and a soul.
Both Storious and Legeiel being around as the opponents for Saber Primitive Dragon's debut fight could signify as both of them being Evil Counterparts to Touma.
It's a bit late, but the reason why all the Riders have copies of their Seiken on the suits is because they're attempts to recreate Saikou which literally turns the user into the Seiken.
Many people have been saying that the Opening and Ending songs should be the other way around, but actually they're the right way. The history of Saber's world is written in the Great Book, and books in Asian countries are read right to left instead of left to right, the show is like a Japanese book! The only reason most don't figure this out is because "reading the book" backwards is impossible, because it's a tv show and not an actual book.
How do the book themes fit in with the elemental powers of their respective Seiken? Well...
Kaenken Rekka (Fire):
Brave Dragon: This one's a no-brainer as a lot of dragons are said to be fire-breathers.
Storm Eagle: This could be a reference to the phoenix which is a mythical bird often associated with fire. In addition, both eagles and fire symbolize wisdom and power.
Saiyuu Journey: The Samadhi fire was an essential element in Sun Wukong's story as it was originally meant to execute him when he was imprisoned in a cauldron containing it for 49 days, but he survived by hiding in a corner, and he used its heat to make himself more robust. In addition, one of Sun Wukong's abilities translates to "FIERY eyes, golden pupils".
Suiseiken Nagare (Water):
Tenkuu no Pegasus: In Greek mythology, Pegasus is the child of Poseidon, the god of the sea.
Lion Senki: This one's ironic given that a lot of cats don't like water. However, this could be a reference to the merlion: a mythical creature that's half-lion, half-fish, and is the mascot of Singapore.
Peter Fantasista: Peter Pan spends his eternal childhood in Neverland, which is surrounded by water.
Raimeiken Ikadzuchi (Lightning):
Tri Cerberus: In Greek mythology, Heracles was the son of the lightning god Zeus, and his final labor was to bring Cerberus to King Eurystheus.
Needle Hedgehog: Hedgehogs with their round and fluffy bodies do resemble thunderclouds.
Lamp Do Alangina: The Disney adaptation of this story has the villain identify the hero via an artificial lightning storm.
Dogouken Gekido (Land):
Genbu Shinwa: Genbu's a tortoise with a snake entwined around it. The shell of a tortoise does resemble a rock.
Jackkun to Domame no Ki: The primary object of this fairy tale is a giant beanstalk. Plants are said to be an earth-based ability.
Fuusouken Hayate (Wind):
Sarutobi Ninja Den: Ninjas are sometimes portrayed as having wind-like speed and kites that let them carry out missions in the air.
Kobuta 3 Kyodai: The main way the big bad wolf destroys the pigs' homes is by breath as strong as hurricane winds.
Onjuuken Suzune (Sound):
Hanselnuts to Gretel: Hansel and Gretel overhearing their stepmother's plans to have their father abandon them in the woods was what led them to formulate their plans to find their home again.
Bremen no Rock Band: This one is also a no-brainer. Musicians rely on the sounds of their voices and instruments to perform their songs.
Ankokuken Kurayami (Dark):
Jaaku Dragon: As Calibur is meant to be the dark counterpart to Saber, it makes sense that they share similar motifs.
Kougouken Saikou (Light):
Kin no Buki Gin no Buki: Light is often said to represent good morality while this story teaches about getting rewarded for being honest, a must for good morality.
Eneiken Noroshi (Smoke):
Konchuu Daihyakka: It makes sense when you remember that smoke helps calm insects.
Jikokuken Kaiji (Time):
Ocean History: The earliest life on planet Earth started in the oceans.
Mumeiken Kyomu (Void):
Eternal Phoenix: Though void isn't what many would expect for an element being tied to a phoenix, there is something clever at play: phoenixes essentially have an infinite life while the Japanese word for infinite, Mugen (無限), features the kanji used to represent the element of void in this show's context (無).
Amazing Siren: Tying in with void being the power to cease or negate something, sirens have been known to end the lives of sailors who would dare fall for their voices.
Kokuranken Shikkoku (Black):
Gaikotsu Ninja Den: A common misconception about ninjas is that all their outfits are black. In addition, the color black has symbolisms that match Desast's motifs: antagonism (Fenrir), power (Japanese Tiger Beetle), and death (The Singing Bone).
Seems the reason Kento couldn't see the good outcome of his vision twice is due to Kurayami being a sword of darkness, and therefore being unable to account for light's intervention in its entirety.
The first time it never accounted for the fact that Touma could bring Primitive Dragon to calm down, the light here being part of one of the elements that is natural to Brave Dragon and a part of Elemental Dragon: Fire. It never expected Touma to go through light (Primitive Dragon's flames) to reach the darkness (Primitive Dragon) to create a new light (Elemental Dragon).
The second time it never foresaw that Rintaro would be able to draw Nagare's light, it was merely relying on the darkness of Rintaro's heart to make a prediction that eventually failed to happen.
The truth of the matter however comes to light in Chapter 45: Everything that happened, is happening, and is supposed to happen is written in the Omniscient Tome, even the World's destruction, but Luna (being a part of said tome) knows Touma has the power to create things that are not in the Tome. In other words: Kurayami was capable of reading from the Omniscient Tome and showing the future to Calibur.
The artwork of Sarutobi Ninjaden Wonder Ride Book mirrors that of the 12th arcana of the tarot deck, The Hanged Man. It's owner, Ren, has been displaying traits of the reverse Hanged Man, like having a resistance to change and being unable to make decisions on his own. This could partially explain his behavior after Kento's supposed death.
The Reveal of Chapter 36 gives Tassel's fixation on Touma and his adventures a lot more sense given the fact the he's observing the man prophesied to be his successor.
Why does Xross Saber break the trend of a Seiken and Wonder Ride Book combo? Because Solomon has it (if an incomplete version) from his ritual, and the two are fighting to see who will ultimately obtain the full power to change the world. So Touma has the Seiken, but Isaac has the WRB.
Isaac's full name, Isaac Kanda, was revealed by secondary writer Keiichi Hasegawa in a tweet. Notably, unlike the Seiken wielders, Isaac's surname has an archaic Alternate Character Reading of the Kanji for god (kan, as opposed to the conventional kami or shin — e.g., Touma Kamiyama, Reika Shindai) in it. This ties well into Isaac's god complex and megalomania, as well as the fact that he doesn't wield a proper Seiken, instead using either purloined swords or his Evil Knockoff sword Caladbolg.
Zocks's appearance in the Special Chapter sheds light of another brilliance: Twokaiser is based on the pirate-themed Gokaigers, and along with Zocks himself and his siblings being World Pirates, pirates are sword-wielders themselves, similar with the Riders in this series.
It's fitting that in the end, the conflict was between a writer (Touma) and a story (Storious).
Expanding on that concept, Storious's backstory and motivation is anchored on the idea that "nothing is original" and "everything is a cliché"; while Touma's motivation is anchored on the idea that "we can have fresh takes on well-worn ideas".
The swordsmen's alignments are based on whether the elements representing their Rider forms produce light:
Touma and Yuri's elements, fire and light, both produce light, and they are firmly on the side of good.
However, a fire that's burning inefficiently generates copious amounts of light-obscuring smoke. Unlike Touma, who tried to persuade his allies to help him search for the traitor, Daichi decided he couldn't trust his fellow swordsmen and became an Anti-Villain and the wielder of Kurayami as a result.
Kento's element, Lightning, produces light, but lightning is produced by dark clouds; this foreshadows his fall into darkness and subsequent use of Kurayami.
Rintaro, Ogami, Daishinji and Ren's elements, water, earth, sound and wind, do not produce light, but do not obscure light either; during the traitor arc, they acted as Unwitting Pawns to the current, more sinister Master Logos.
Kurayami has darkness as its element, but its name contains the kanji for "moon", and Jaaku Dragon's transformation has the word "moonlight" in it, suggesting a secondary motif of the moon; fittingly, three of its users are anti-villains.
Kurayami has the distinction of being used by characters of all alignments, from heroic characters like Yuri and Sophia to the irredeemably evil Isaac, which makes sense since, like the moon going through phases by reflecting sunlight, it only reflects the light (or lack thereof) in the user's heart and isn't an inherently evil sword on its own.
Reika's element, smoke, can obscure light, but not completely, and she's a Well-Intentioned Extremist. Whilst Ryoga's element, time, may be a subversion, Durendal has a secondary motif of the deep sea, which is characterised by absence of light unless something produces light in it; Ryoga, whilst also well-intentioned, is more rigid and resistant to change.
Bahato's element, Void, can be seen as a lack of energy, or a black hole, which signifies an absence of light. Bahato, whilst a Tragic Villain, distinguishes himself by his refusal to change, and thus can never see the light. This separates him from the rest of the Saber Riders in that, whereas they eventually fought for the light and their swords are added to the Xross Saber, a sword characterized by space and stars which emit light, Bahato never did and as such, his sword could only form the skeleton of Xross Saber. As for the Trio of Deep Sin, all of them only plunged into evil after being traumatised by loss due to the swordsmen's collateral damage, much like how a light-emitting star would become a light-absorbing black hole.
By contrast, neither Isaac or Storious considered themselves swordsmen nor are they directly associated with any element. They're not only easily the most villainous of the Riders, but their corrupted personalities also give them some metaphorical perception of their definiton of light (Isaac's God complex and Storious considering "endings" to be beautiful).
Aside from sharing a writer, there are two other reasons for Ghost to cross over with Saber.
It would seem that Saber, Blades and Espada each have their basic Wonder Ride Book that they absolutely need to use to transform, as implied with the form-creation website automatically placing the basic Ride Book of the selected Rider into the SworDriver and not allowing it to be swapped out, as well as the SworDriver not giving any special song for using Tenkuu no Pegasus and Peter FantasistawithoutLion Senki, considering the resulting form a generic non-elemental form.
Espada might fall into Can't Catch Up due to being unable to use any other Fairy Tale Ride Books besides Lamp Do Alangina, unless he's allowed to borrow Divine Beast/Sacred Animal Ride Books from the other Riders, which already exists in quite limited numbers due to them all being tied to specific existing Riders.
This may very well be the reason why Kento was Put on a Bus. And became Calibur III.
However, he also eventually got his Wonder Combo Golden Alangina form via Tri Cerberus, Needle Hedgehog and Lamp Do Alangina. Somewhat ironically, Can't Catch Up still applies anyway because Touma and Rintaro both have obtained forms with higher power than a Wonder Combo during the time Kento is "stuck" being Calibur.
Storious' The Fourth Wall Will Not Protect You monolog at the end of Chapter 40 implies that he became the true personification of storytelling, a natural part of human existence, language and culture. People make some sort of narrative everywhere, everyday. It truly drives home that he has become a god.
. Notably, unlike the Seiken wielders, Isaac's surname has an archaic Alternate Character Reading of the Kanji for god (kan, as opposed to the conventional kami or shin — e.g., Touma Kamiyama, Reika Shindai) in it. This ties well into Isaac's god complex and megalomania, as well as the fact that he doesn't wield a proper Seiken, instead using either purloined swords or his Evil Knockoff sword Caladbolg.