Several of the pins and brands have multiple hidden meanings in them:
While you might know that the brands are designed to match the animals of Chinese Zodiac, their shops are also introduced to the player in their official order, give or take "natural" progression through the game: Mus Rattus (Rat) and D+B (Ox) are the first two you become familiar with, and Wild Boar (Pig) is the last. Gatito is not available during one's first playthrough, since it represents the Cat that was "left out" of the Zodiac.
The "Wood, Wind, Fire, And Mount" pins not only contain a Sun Tzu reference, they're also the Three Wise Monkeys (plus "Do No Evil") done with the Gatito mascot.
If you look at the Lightning Arrester pins, you will find a recurring theme: The Pegaso ones are named respectively "Thunder Rook" and "Lightning Rook", the rook being the chess piece representing a tower, while the "Electric Warning" pin from Mus Rattus shows the drawing of a radio tower on it. A tall tower is the structure most likely to be hit by lightning during a storm. Interestingly enough, the Tower card in Tarot (representing cataclysmic change) - one of the best-known cards, in fact - is traditionally drawn as a tower being hit by lightning.
While Word Of God states which pins they are actually using, Shiki and Joshua fight by controlling and throwing around objects, respectively (the "Sexy" line of pins of D+B and Dragon Couture's "Live Slow, Die Fast"-pins respectively), and Beat launches death from above (Wild Boar's "Fly" and "Fresh Line" pins). Their attacks weren't just chosen randomly, they're fighting with psychs from their signature brands. This can somewhat apply to Neku as well. Jupiter of the Monkey pins are great for beginners, and at least one of their threads has "They're Neku's favorites." in its description.
The Gatito pin sets all differ in deck real-estate. Gatito: 1 pin. Nexus Ray: 2 pins. Over The Top: 3 Pins. Irregular Note: 4 pins. Holy Field: 5 pins. Darklit Planets: 6 pins.
There are 7 trade-only pins (Scarletite, Rare Metal, Tektite, Adamantite, Orichalcum, Shadow Matter, Dark Matter), and each of these pins sports a different number of gems. One for Scarletite, two for Rare Metal, etc., and if you rearrange them in a numerical order you also get the 7 colours in the order of the rainbow. You encounter these pins in the game in numerical order, and they also represent the expanding amount of effort you will have to deploy to obtain them. While the game shoves Scarletites in your hands merely for making it to the end of the daily mission at first, the difficulty in gaining more ramps up significantly once you exhaust the mission-related supply... so the difficulty rainbow loops back up to Scarletite in the post endgame!
Game Masters' names:
Each of the Game Masters' names has one kanji that shares a major radical, or piece, with their Cantus form. The "yo" in Yodai is 洋, which has 羊, or sheep in it. Minamimoto's "moto" is 師; lion is 獅. Tiger is 虎, and the "ko" of Konishi is 虚 (which means "non-existent/illusion", another reference to her Noise form). Finally, Megumi Kitaniji's full name is 北虹寵, which can be rearranged to form 蛇, "snake", or the kanji for dragon, 龍.
In addition to that, their names also include the four cardinal directions. Not only that, but they go clockwise. First you face Yodai Higashizawa (East). Next is Sho Minamimoto (South). Then Mitsuki Konishi (West) and last Megumi Kitaniji (North).
Also, they all fit "____ No Evil". From Sho being long-winded and hard to understand (Hear No Evil), Konishi's hiding in the shadows (See No Evil), to Kitaniji never Speaking of the real Game that is going on, and Higashizawa is the least "evil" of the GMs (Do No Evil). For bonus points, the special pins they drop on Ultimate show these exact principles.
Sometimes he makes sense. He calls Players "binomials" because they're in pairs.
Minamimoto's health levels are references to pi. His boss fight has 3141 HP, and his Taboo form has 5926 HP.
The zetta prefix that Sho is always using refers to 10^21... in other words, a SEXtillion. Sho is probably aware of this. So in other words, every time he says "So Zetta Slow!", he's essentially saying "so fucking slow", just with math puns.
Joshua's death line is "Neku, how could you". You would think it's just about the fact that you screwed up and got both of you killed. It's actually that you failed him because Neku is a key pawn in his grand plan.
The barrier of the Shibuya River is in fact the symbol of Anguis Canuts — a.k.a. Megumi Kitaniji's Noise form. It was a rather subtle hint of who was really waiting for you, and, to a certain extent, who was really in control all the time Neku was involved in the Reapers' Game. One of the areas at the end of the Shibuya River is named 'Rubicon', and the saying 'Crossing the Rubicon' is an idiom for Point of No Return. When you reach the Shibuya River and it's 'Rubicon' area, the characters are literally at 'the point of no return', in both the trope, and for themselves — Neku couldn't enter the game again, and was pretty sure that he was screwed due to all his 'rule breaking', Beat was fading away due to his misbehaviour as a Reaper, Joshua was erased (or so they thought), Rhyme was stuck as Noise conjured by a pin, and Shiki was was stuck as Neku's entry fee — so they could only keep going forward to try and take down the Composer, or go down trying. Also, the Rubicon from the phrase was a river that was crossed — and that's exactly what it is in-game, too.
Kariya at one point calls Joshua "The Petit Prince". A reference to the story by Antoine de Saint-Exupéry, yes? In the book, the eponymous prince is described as a boy who "asks lots of questions, and ignores the ones that he is asked". What is Joshua's defining trait for most of the game? One of the key points in that story was also that to befriend the fox, the Prince had to get close to him in small, daily, incremental steps in order to build trust, and that with that trust friendship could exist. What was the point of this game again?
In Another Day, Joshua insists that he be called Pink, and tells Shiki to be Green. His reasoning is that it's the colour of her skirt. However, the colour green is often associated with envy (as in, "green with envy"). If you think about her self-esteem issues and her jealousy of Eri, it suddenly makes a lot more sense that she is Green.
At the startup screen where you select "New game" or "Continue", "New game" is the Red Skull Pin and "Continue" is the black Player Pin. If you're starting a new game, you begin as a living person by taking the red pin, and if you're continuing, you take the Player Pin because you're already dead and playing the Game!
Neku is shown keeping his head down, lost in his bubble with his headphones on as he walks through the crowded Shibuya streets, the game trying to show that he should take those off and learn to see the people around him. Have you looked at yourself while you play this game in public?
While he seemed to have a flair for the classic dramatic gesture of Milking the Giant Cow, it turned out that Kitanji was actually looking into his left hand to see how much time was remaining on his game timer.
Tigris Cantus has 4444 HP; that's Four Is Deathtimes four. Plus it is the Noise form of Konishi, and in Japanese "shi" is pronounced like "four".
The song "Game Over" starts playing midway through Week 2, on the day that Makoto is pressuring Eiji Oji to shill his new ramen shop — comparing the lyrics to the events of the day, one could say that "Game Over" is actually Oji's character song.
Neku listens to music a lot, and his name, roughly, means sound.
The soundtrack itself is also a bit of Fridge Brilliance - of course it sounds like that. Because it's what Neku's listening to on his headphones It also explains why the game menu music is changed by selecting a record purchased by Neku in a music store. This music is what Neku is listening to in between battles
Kitaniji (and presumably everyone else in the UG) treats the Composer as God. While this seems to make perfect sense at first glance, it becomes a little confusing once you find out that the Composer is actually beneath the Angels in the celestial hierarchy. But then you remember that the Secret Reports also make it clear that everyone in the UG except for the Composer himself is completely oblivious to the fact that the Angels even exist. Because of this, it makes perfect sense for them to think of the Composer as an omnipotent God; for all they know, he's the highest being there is.
Know why you hate the first few days with Joshua? When he can't float, he only deals damage at the end of the combo, so he deals a lot less damage for all your button mashing, and your pins end up dong all the work. It's literally more frustrating just having him as your partner instead of Shiki. And that super-long, smug explaination about the first mission? You hate him because he's literally explaining everything you already know. You're set up to have your feelings change about this guy from the beginning. That and he's making do all the dirty work, because he's outright not even trying.
Similarly, Beat's personality can be seen in his gameplay. Beat has a severe lack of foresight, and he is consequently a Glass Cannon, dishing out plenty of damage but unable to take a hit. In addition, while his combos make it easier to reach fusions and turn the tide of battles quickly, they have the potential to do heavy damage if used incorrectly.
All the Players really dislike BRAVE+. It's a medicine, It isn't meant to taste good.
Joshua allowed Neku to scan him and find out that he killed Neku in order to make Neku not trust him. After all, his plan was based on the fact that humans can't change, so when Neku changed Joshua knew he was losing the game a little. So he just decided to try and make Neku not trust him. But Sho's Level i flare basically put Joshua in a lose-lose situation - lose your proxy, or make him think that you could be trusted and therefore helping him change. Maybe Joshua knew about that and showed Neku the location of the Shibuya River so, if he had to pull the sacrifice card, Neku could still go on and try and defeat Kitaniji for him.
In terms of communication, the term "noise" refers to any disturbance or interference that impedes the communication process. Given the themes of the game, this may not be coincidental. It's also slang for things we ignore because we don't want to listen.
At first it seems like Neku being able to use every type of pin is just another example of One Hero, Hold the Weaksauce. But when you take into account that Neku is Joshua's proxy, well, naturally Joshua would want 'his player' (so to speak) to have some sort of advantage, and could have easily fiddled things a bit, making Neku able to use every pin. Or chosen him in the first place because of that ability. This is hinted at in universe; when Kitaniji first hear's of Neku's success after week one, he makes a cryptic remark about how of course His choice would be talented.
About the music in the game, and Neku also being "sound". It can be said that the music heard in the game is music that Neku is listening to on his music player, which is probably sung by artists signed to CAT's label, since Neku tells Joshua that CAT also does music and video. In the end this makes sense, since each song in the game fits every situation, and people are known to do that with songs that are special to them.
The name Neku. It is one letter away from "Neko", the Japanese word for cat. While this can be seen as a subtle nod to his intrest in CAT's artwork, it can also been seen as a foreshadowing of his character development. Cats are generally seclusive, secretive and at worst, distrustful. However, overtime, given enough dedication and effort, they begin to open up to their owners/ other living things.
Consider Joshua's name. Joshua in Hebrew is Yeshua, which in Latin, translates into Jesus. Now who was the composer again?
The level down mechanic available in the game. Neku is slightly lowering his vibe to limit his power, just like the Composer did, but at a mostly insignificant magnitude
Joshua and Neku's level three fusion has them dropping the moon-exactly what Minamoto said he'd do. Minamimoto wants to become the Composer. This is one of the hints to Joshua's true identity.
The game rewards you for taking breaks of up to 7 days by giving your pins exp while the game isn't being played. Why? Because the entire point of the game is to stop being wrapped up in our own worlds and go out and experience other people. The breaks are incentives to put down the game and go talk to others!
Why Neku has two Player Pins: One for being part of the Conductor's game, and one for being part of the Composer's.
Neku levitating and strangling Shiki may not be cutscene power to the max after all. His only telekinetic pin at the time is Psychokinesis, which only controls inanimate objects. Wait, clothes are inanimate objects...
The reason why Shiki looks at a picture of her and Eri on the phone a lot is because her price of entry was her appearance. She's doing so that she doesn't forget what she looks like.
When some people die, they go to the "underground" to compete in the "game". If they win, they get back to the real world. So what happens? Do people just forget that the person died? Do they accept that someone came back from the dead? What?! Presumably it's the reason the Composer is required to have so much, and such powerful Imagination; it literally has to rewrite reality so that the people who win the game never died. The only ones who would then know of the week they spent dead would be the dwellers of the UG, the player, and the player's partner who, presumably, was also returned.
It's no surprise that Sota and Nao are dead, since all players are. However, when Makoto is promoting the red pins, they're the first he sells to. Living people can't see the players, so the two must be alive. You get to see Sota and Nao before they die, and it can be a bit jarring to realize that during later playthroughs.
The shopkeepers all grow attached to Neku; at least two of which actually want to take him out on a date, and one who wants to introduce you to his grandson. However, Neku is dead - if they tried to follow him out of the store, he would simply vanish before their eyes. If they tried to look him up somehow, all they'd find is a story about how he got shot in a back alley near some CAT graffiti. (Of course, perhaps Joshua disposed of the body, in which case it would be a missing person report instead. Then it would become Fridge Logic instead as people would have to start looking for Neku in the only place he's been spotted - the shops, offloading vast amounts of wealth for that Silver Baron.)
What'd happen if somebody the dead person knew saw them in the shop? Like, what if Neku ran into his mother or somebody like that? Or better yet, what if Eri bumps into Shiki at say, 104, considering for the first week Shiki has Eri's appearance?