Demikids has your starter Mon. The very first monster you get, and your partner for the entire game, only gains levels by absorbing other monster's exp through fusion. Taking into account that you'll likely need most of your other monsters for fusion, you'll usually end up just mass fusing dozens of cheap monsters to get your starter to level up. To put it differently: This is like getting a Pikachu that has to devour its opponent every time it wins a battle. By the end of the game, your starter is essentially a walking mass of hundreds of souls.
On the other hand, if Mastema is telling the truth in the Clipped Wings DLC, there is hope for God.
A common goal of Chaos factions is a world where Might Makes Right, i.e. the strong rule over the weak. Now here's a frightening implication: What if you're handicapped/disabled, or worse, born as such? You are screwed to begin with.
Plenty in the demon's designs. The monster design brings forth references to the mythological being it's based on, to other games in the series and sometimes to pop culture as well.
Once you get over Mara's face, you should notice it riding a golden chariot with many sharp blades. Then you realise it's the embodiment of our dark desire - lust, greed and violence.
At first, it's weird seeing how Angel - a Divine being - is dressed in the series. It makes sense once you notice that she also wears a leash. After all, they are guardian angels that are bound to a human being on birth. They are also blindfolded, possibly as an ironic reference to 'watchers'.
Melchizedek. By far one of the most outlandish angel designs, but makes a whole lotta sense when you think of it.
First off, he looks and acts more like some kind of Super Sentai hero than an angel. Well, he's the King of Justice. Just try saying that out loud.
Second, he's faceless. In the Bible, Melchizedek is described as "without father, without mother and without genealogy".
Inanna. Moreso in the original concept art, but there are a lot of details. According to the various versions of Inanna's Descent to the Netherworld, Inanna was wearing seven of the following: wig, crown, turban, ring, beads, lapis lazuli necklace and measuring rod, girdle, mascara, bangles, dress, and earrings. In the final version, while some are harder to see than others, she's wearing the wig, turban/crown, earrings, bangles, necklace, and her boobs might just be beads. Previous versions had even more of the above. The decorative piece on top looks a lot like a female sign, which is also a sign of Venus. Venus is not only a love goddess like Inanna, Inanna was also represented by the planet Venus.
The series-wide interpretation of YHVH, patron of the Law path, actually makes a lot of sense if you look at it from a Japanese perspective. Unlike most Westerners, Japanese individuals have very little truck with Christianity; it is, and has always been, a tiny and easily ignored cult, rather than the huge society shaping element it is in the West. Consequently, a lot of things that Westerners look past due to subconscious indoctrination into the faith is highlit for Japanese due to the Values Dissonance. Throughout the Old Testament, God demands repeatedly the respect, reverence and worship of humanity, and in it blind obedience to God and his desires is held up as the ideal to which humanity should adhere — from the Ten Commandments, which place importance on obeying YHVH and doing what he says, to his own admission of being a jealous god. Take, for example, the infamous story of Abraham, one of the tales from the Old Testament that Christians often sweat over and which many atheists and antitheists are quick to call out. In this story, Abraham comes within a heartbeat of cutting his son Isaac's throat and making him a Human Sacrifice, only for YHVH to change his mind at the last second. And the story holds up Abraham's willingness to murder Isaac because that is what God told him as something to respect to admire, that his blind loyalty is a trait one should attempt to emulate in its fervor. In a later story in the Old Testament, YHVH fails to stop a father sacrificing his daughter in thanks for a God-granted victory, as he had promised to do. It's very easy to see why someone not culturally inclined to accept either parable as a holy tale would be able to extrapolate YHVH as the sort of monster who wishes to reduce all of creation to nothing but endless, unceasing, mindless praise of itself.
The ending of the Law path throughout the series is also a very fitting; although people have been indoctrinated to think that Chaos Is Evil and thusly Order Is Good, the truth is that an extreme of either would be awful. A world of total order would pretty much require the complete obliteration of independent thought, emotion and chance of all kinds. In fact, the Shin Megami Tensei version is actually a pretty optimistic depiction of what such a world would look like; an alternative interpretation of such a world would basically be a void. Absolute nothingness: no variation, no transformation, no creation, no destruction. Just infinite. Total. Unending. Emptiness.
The ending of Persona 2: Innocent Sin, is similar to the plot of Nocturne. In Innocent Sin, Maya's death triggers the end of the world, and then the four remaining heroes create a new world where everything went well for them. In Nocturne, the Conception requires someone with a powerful demonic sponsor, a lot of Magatsuhi, and a Reason. In Innocent Sin, Philemon was the sponsor, the protagonists produced Magatsuhi from the pain of losing Maya, and their Reason was to make a better world.
After defeating Vishnu in SMT 1, he bemoans the fact that the one who defeated him wasn't an avatar or a demon, but a Badass Normal human. The main character is implied to be the reincarnation of Adam. In comparison to Nakajima being the god Izanagi, Adam was just a human, and his name literally means man.
According to a guidebook for the first game, demons that repel physical attacks do so by making an illusion that their opponent is attacking the demon when they're actually attacking themselves. This is why the Demi Fiend's Pierce ability doesn't let him attack physical repelling demons. Pierce gives all his physical attacks an Armor-Piercing Attack quality. It doesn't do anything about illusions.
The Demi Fiend's Javelin Rain features him using a Roundhouse Kick to throw lasers. This isn't without precedent; the Gae Bolg, of Celtic fame, was a spear that had to be thrown from the foot.
Oshichi is a random encounter that appears on the overworld of Shin Megami Tensei I, but only before the nukes. Oshichi is a demon that appears before fires start.
The Demi Fiend, in his stint in Digital Devil Saga, is not immune to earth magic. Part of that is because the Masokados Magatama only protects from elements that were in his game, but technically the earth can damage him in Nocturne. The Demi Fiend takes damage if he jumps off of Mantra HQ, even if he's immune to physical damage. It's Not the Fall That Kills You; he takes damage from hitting the earth.
Nocturne is unusual in the series for not having Law/Neutral/Chaos based endings. But all of the Reasons can relate to Neutrality. They're deconstructions of why the player would pick Neutral in SMT 1.
Shijima, the Reason of Silence: Hikawa's goal is the eradication of emotion, self, and passion, for the sake of a logical and harmonious world. In the context of SMT 1 Neutrality, Shijima is killing Law and Chaos because both sides are insane and illogical. Law and Chaos go to war with one another, kill innocents, and generally make a nuisance of themselves. Hikawa initiating the Conception is similar to the Hero and Heroine killing the leaders of the Messians and Gaians; lots of people die in the process, everything is in upheaval, and those left have to fend for themselves. Hikawa is also a charismatic demon summoner with strong connections to computers, traits that the Hero needs to survive.
Musubi, the Reason of Solitude: Isamu wants everyone to live isolated, with no interference from one another. He's also very hypocritical in this respect; he gains power from channeling spirits, uses the Amala Network (which is the most interconnected thing in the entire Vortex World), requires the Demi-Fiend's help in defeating the demons of the Amala Temple, and sacrifices Hijiri to summon Noah. Musubi is Neutrality by rejecting the thoughts of others. Rather than disagreeing with the philosophy of Law or Chaos, which is Shijima's way, Musubi is about disagreeing with the characters themselves. In the context of SMT 1, it's rejecting the Law and Chaos heroes, or not feeling the Player Punch when the Hero kills them. However, if the Hero of SMT 1 embraced this philosophy, he would also be a hypocrite, because he fights with the Heroine and his power is summoning demons to his side.
Yosuga, the Reason of Strength: Chiaki wants a world where the powerful can do what they want with the weak. It's also unusual within the series because survival of the fittest is a Chaotic ideal, and yet angels embrace it. With Law counterbalancing Chaos, it's Omnicidal Neutral at its finest. In the context of SMT 1, it's how the Hero and Heroine legitimize Neutrality: they killed everyone who opposed them.
The Temple and Tartarus are prominent towers. The heroes discover the truth of the world after climbing to its top at the climax, although they need more explanation of what happened during the sequels. Sera and the Embryon confronts Angel, SEES fights Nyx Avatar.
Everyone in DDS, except for Sera and maybe Cielo, is an adult, at least physically. SEES consists of teenagers, a child, a dog, and a robot.
Aigis and Koromaru are the only nonhumans on the team. Sera and Roland are the only non-AI party members.
Junpei and Yukari have similar attitudes towards their Persona powers as Heat and Argilla do towards their Atma. Junpei and Heat love their new powers, and they also have similar affinities (fire and physical attacks). Yukari doesn't hate her powers like Argilla, but she laments that the power to stay awake during the Dark Hour is like losing your innocence. Fittingly, they're both healers, but with opposing offensive magic (Yukari has wind, Argilla has earth).
Fred and Ken are children who hang around the party, even though Ken is a fighter and Fred just tags along. Some members of the party are responsible for the death of one parent, although arguably it's not their fault. Fred's father Greg/Lupa went insane and had to be put down by the party, and in a way he was already dead. Ken's mother was killed by Shinjiro in an accident.
Strega is Sera's Shadow Archetype. Both are disposable lab experiments in a series of tests with a high death rate, starting when they were children. As a result of these experiments, none of them have long to live. However, Sera realizes this and chooses to fight to save the world no matter how ill she is. Jin and Takaya want the world to die with them, powers intact. Chidori tries to remain indifferent so that she won't be sad before she dies.
The people behind the abuse of Sera and Strega appear to be trustworthy, have similar goals, and the same circumstances of death. Real Serph looks almost exactly like Serph, and Ikutsuki was thought to be a trusted adult. Real Serph wants godhood, and Ikutsuki wants salvation and power. They die outside of battle, long before the climax, in a cutscene where the person pointing a gun at them is shot, and that gun isn't the direct cause of death. Real Heat threatens Real Serph with a gun and is shot by Real Argilla, which upsets Sera so much that Brahman corrupts the data around the area, which turns Real Serph into Varuna, and his rampage forces the Karma Society to kill him. Mistsuru's father shoots Ikutsuki but is shot himself, and Ikutsuki falls off of Tartarus while injured. Their actions and manipulations leave behind a huge mess that the protagonists have to clean up.
Someone betrays the party after being manipulated, but ultimately sides with the party. Coincidentally, they're both weak to electricity. Heat betrayed the party after discovering what the real Serph did, and he's fought as Vritra. He loses his weakness to ice and gains one for electricity. Aigis is controlled with a remote control, and has a natural electricity weakness due to her mechanical body. Heat rejoins the party if enough conditions are met, and Aigis rejoins anyways.
The Final Boss of Digital Devil Saga is found on the Sun, and the boss of Persona 3 is the Moon.
The protagonists both die, but it's not really the end for them. Serph is reincarnated, and also journeys across the worlds as Seraph. Minato becomes the Great Seal, and there is hope of his release.
Nocturne is the only mainline game where the hero does not gain the power to summon demons from Stephen. But the Demi-Fiend gains the power to summon demons from another old man in a wheelchair.