6 Brahma
In many religions and mythologies around the world their is a trinity of sorts between three main dieties such as Zeus, Poseidon and Hades of Greco-Roman mythology and Odin, Villi and Vi in Norse mythology. Their is also such a trinity in Hinduism, one of the most represented cultures in Shin Megami Tensei, those being: Shiva the destroyer, Vishnu the preserver, and Brahma the creator. Yet while both Vishnu and Shiva have appeared in dozens of titles, Brahma hasn't appeared sense the Devil Children series, matter of fact, Brahma hasn't actually appeared in any mainline games at all, the closest being Kyuaku Megami Tensei, a SNES title re-release of the original Megami Tensei and Megami Tensei 2 bundled together, the spiritual prequel to the Shin Megami Tensei series. Heck even here he was just a replacement for Brahman, a demon based off of a concept in Hinduism closely associated with Brahma, who's had even less appearances. According to the wiki Brahma has to date only appeared in 8 games, four of which were two separate pairs of the Devil Children series, and another two being the Persona 2 duology which shares a lot of demons between them.
What's bizarre is that Brahma is supposed to be the third in the trinity that includes Shiva and Vishnu, two of the most recurring demons in the whole franchise. Shiva is the only demon to have consistent fusion material for his special fusion in the franchise, Rangda and Barong, the respective leaders of the forces of Evil and Good in Hindu Mythology, and this method has been a tradition in the games sense the very first Shin Megami Tensei in 1992. In fact I'm pretty sure that the only game in the past twenty years that Shiva has been absent from is Digital Devil Saga 1, and if Vishnu has appeared in at least one game of every spinoff series except for the Devil Survivor series, and has appeared in every mainline and Persona title. The only recent game that might have either of them absent in P5S, which is not listed in either demon's appearances section of the wiki, but was also a fairly recent release at the time of this writing and which I have yet to play, but also would find odd to not have at least a staple like Shiva included.
Shiva and Vishnu were to of the best demons in my first playthrough of Nocturne. Vishnu had high enough stats to unlock most of the doors in the fifth Kalpa of the Labyrinth of Amala that required demons of high stats without being buffed by the Mitamas, and both are such a powerhouses that I used them together and they helped me take down both Kagutsuchi and Lucifer, even without having pierce. To have a third member of the trinity, just be non-existent in the majority of games just seems so bizarre to me.
5 Kvasir
Norse mythology is one of my all time favourite mythologies, and while not as represented as Hindu or Abrahamic mythology, Norse is still pretty common, but for some reason it also has a lot of demons based off of Norse figures or concepts that have only appeared once and are than forgotten about. Kvsair has so far only appeared in a single game the second Majin Tensei game, meaning that he hasn't had an appearance sense 1995, meaning that he is one of the oldest to suffer this fate, and long overdue for a new appearance in my opinion.
Kvasir is one of the most important of the Vanir, one of the two tribes of gods in Norse Mythology, the other, more represented Aesir, consisting of Odin, Thor, Loki, Sif, and Baldur to name just a few. The difference between the two was that the Aesir tended to be the more civilized, while the Vanir were more connected to living off of the land, and like many Norse concepts and values, to the modern, heavily Christianized perspective of today, they seem contradictory in nature. Many ancient sources on the topic and concept lost to time also raises many questions as to whether or not the likes of Freyja and Frey, who were born to the Vanir were even considered or thought of as a part of the tribe.
Kvasir, considered to be one of the most important Vanir, is a sort of a mixture between these two tribes, as he was born when the saliva of the two mixed after the war between the two tribes ended with a truce. He is the god of wisdom and poetry, and according to the myth humanity learned poetry by drinking mead made from his blood after he was killed by two dwarfs, one of which actually made an appearance in Persona 2. Odin, relentless in his pursuit of knowledge above all else than worked for many months to try and obtain the mead after it was hoarded by the Giant, Suttung and after stealing it returned to Asgard where he shared it with the other Gods.
If I had to make up an excuse for him to be put into the game, than I could easily see either defeating him in a boss fight or negotiating with him for his blood to be a part of a challenge quest to give Dionysis a bizarre wine to taste like how you needed to ask a Zhen to give you a feather in Strange in Journey.
4 Munin and Hugin
In Norse mythology Munin and Hugin are the two ravens and accompany Odin, and are associated with the concepts of 'memory' and 'thought' respectively. Both are sent out at dawn and return in the evening, or by breakfast in some sources, to report back to the God eternally lusting after knowledge, and relentless in obtaining it. I know that I am cheating a bit by putting both in the same spot on this list, but they largely serve the same role in mythology and I could easily see them be interchangeable game-play wise as well, maybe be encountered at the same time, needing to recruit both both at the same time, or have already fuse the other to recruit the other, be used together to make a special fusion and maybe even the developers can give them each a weakness, and that they repel or absorb what the other is weak to.
Call me biased for my love of black bird symbolism, and Norse mythology, or just that I find their devil children designs to be amongst the most adorable in the franchise, its my list. Like I said in the last entry, Demons based off of Norse figures or concepts that have only appeared once and are than forgotten about, in this specific case, their first appearance was in Majin Tensei Ronde in 1997, but unlike Kvasir they actually did get another appearance in Devil Children Fire Book & Ice Book, which is where the image you see on screen is from, sense the wiki doesn't even have an image for them in Ronde, and their Devil Children Designs are so adorable in my opinion that I wish that these were the designs for their return in a future title. Cute is underrepresented in SMT to anything that isn't one of Jack Frost's kin, and I am really in the wrong for wanting more cute from a dark video game series that asks questions morality in the setting of a post-apocalypse that sees friends turn on friends to side with what they believe to be right?
Also like I said when I explained their mythological origins, Hugin and Munin are the companion birds of Odin, who is not only one of the most recurring demons in the series, but was given special emphasis in the trailer that revealed the title with his new Tokusatsu inspired design. Given that Odin, might even be a major component of the plot, his ravens would be a good inclusion, be them as his allies in a boss battle, or as a part of a quest necessary for the plot. Maybe Odin is using them to spy on his enemies during the course of the game.
World-wide birds in the Corvidae family are also closely associated with war and war related deities and concepts in numerous mythologies, such as Badb Catha which in some interpretations is a trinity of war goddesses all closely associated with Raven or crows, Morrigan, Nemhain and Macha. In SMT War is a concept associated with Chaos, and judging from the trailers, SMT V is going to be a chaos-oriented game like Nocturne before it, taking place after the death the God, and with a power vacuum having now risen.
3 Bogle
In Scottish Mythology a Bogle is a benign spiritual creature that exists for the purposes of perplexing mankind, and is the origin of the English phrase "it boggles the mind". There's not much to say about it mythological origins sense that's mostly where it ends, aside from them sometimes also being compared to Hobgoblins, and the mythological entry in Shin Megami Tensei which states that a Brownie will turn into a Bogle if mistreated, but from my understanding and researching both Brownies and Bogles, I couldn't find anything to substantiate it, so this is likely some sort of translation error. Brownies are a domestic spirit that may help the household given a offering, usually of milk and cream and may play pranks if neglected, for their own amusement or on servants who neglect their duties, Bogles pull pranks on occasion, or something that resembles them to an outside viewer, but their nature is not something that most people can grasp, and thus so to are their reasons for their mischief. It is also worth noting that in Scottish Mythology, most spirits are either domestic spirits that aid in housework if rewarded like brownies or are malevolent ones who seek to harm or prey upon people such as the Kelpie, but Bogles, instead are a curious existence that aligns with neither aiding, pestering, giving advice to or bringing harm to mortals.
Compared to most Demons on this list Bogle has actually had a decent amount of appearances, having 11 games in the wiki's appearances section, first appearing in the very first Megami Tensei titles of 1987. However all of its appearances have been in the more obscure spinoffs such as Majin Tensei and Last Bible, its most recent appearance being the 1997 Giten Megami Tensei, and its only mainline numbered entry is the original Shin Megami Tensei. So yeah, unlike most demons on this list, this one actually started as a common recurring demon, that just kind of fell out of use when the nineties ended.
2 Fariedonne
Persian Mythology is perhaps one of the most under-represented mythologies in the franchise. The only two demons who have had a decent amount of appearances are Mithra, and Peri, three if you count Phoenix, a demon that has been categorized into multiple cultures and religions across three continents. The next highest is Dahaka, a dragon from Persian Mythology with nine appearances, but never in a mainline title. Bizarrely many times they actually have a memorable impact on the story and than have very few appearances afterwards. In Nocturne Ahriman is the demon sponsor of Hikawa but hasn't appeared in any game sense, Ahura Mazda joins the party for free in the chaos route of Megami Tensei II, and is the final extra stage boss of Majin Tensei Ronde, but has only appeared in five titles in total all in the nineties, and in Strange Journey Redux Anahita is the first imprisoned goddess fought in the Womb of Grief, which was her third appearance in the franchise to date, but hasn't appeared sense.
The only other Persian demon who looks like it could make it to become a regular is Haoma who appeared in Strange Journey, 4, and Apocalypse, and if you count the re-release of Soul Hackers on the 3DS has made four of their six appearances in the 2010s. Persian Mythology is so under-utilized and represented in fact that with that mention I've already list almost all of the demons who have appeared at all, leaving only four, two of which, Deva and Assassin, are not exclusive to Persian mythology either. If I ever do a list on mythological people, monsters or gods who have yet to appear and should, than I'll definitely include at least one thing from Persian Myths.
Back on topic I think that Fariedonne, a warrior king of Iran who in Persian literature represents generosity, victory and justice, should be the demon from Persian mythology to make an upcoming return for a few reasons. The first is that both Fariedonne and Simurgh have each only had three appearances, making them the ones who should appear sense the others have again, had more and/or more memorable appearances in previous installments. As for my other choice, Simurgh is a bird from Persian Mythology comparable to the phoenix and is probably the reason why Phoenix was even given the category of Persian mythology on the wiki The franchise already has numerous other birds of various cultures that fit that mold that make frequent and shared appearances with Phoenix, such as FengHuang, Bennu, and Suzaku. Their is no shortage of bird demons, two of the more underutilized of which are already on the list and even in terms of birds that represent healing their already exists the likes of Caladrius, while on the other hand historic and/or mythological Warriors, especially warrior kings, who aren't gods are also pretty uncommon to make appearances in the franchise, strange as that may seem. Cu Chulain, and Tam Lin are on the only ones to make frequent appearances as far as I can tell.
Arthur Pendragon hasn't appeared sense Persona 2, and has only made four appearances total not even a third as many appearances as his sword, Excalibur, has made at thirteen. Sir Galahad is the only knight of the round table to have made an appearance besides Arthur, and only as a Persona in the Persona 2 duology, and the Black Knight, a staple enemy or anti-hero knight in literature originating from Arthurian legend has only made two appearances. As such Fariedonne would be a good demon to use to fill two under-utilized concepts at once, while Simurgh would only fill in one, and be barely noticeable as a standout because of how common its archetype is in terms of appearances.
1. Waxwork
In Shin Megami Tensei their is no hard-coded limit to what a demon is a manifestation of. Historical figures, serial killers, the literary canon, religion, conspiracy theories and movie monster you name it, and their is going to be a good chunk of demons who embody them. Their is even a demon called Melissa who was based off of a computer virus that wrecked havoc in the late 90s. While the above five were all gods or creatures of various mythologies in the world I felt that the final one on this list should be something extremely unique, and with personality in its origin and design. This is the demon Waxwork, who has only appeared in two games, Devil Summoner in 1995 and Card Summoner in 2001.
If you don't know what a Waxwork is, its basically another name for a wax museum, a type of museum that usually showcases wax sculptures usually of historical people, but can occasionally refer to other places that display works of wax sculptures and art. My family once actually visited one when I was a kid, and I still remember the museum making an exact copy of my hand out of wax as a souvenir. Waxworks also have a deep connection with the horror genre, with various horror movies of the 20th century featuring wax museums as a setting. This connection likely originates all the way back to the 1800s when one of the first waxworks of England, Madam Trussands, dedicated a section of the museum to having the wax statues depict the true crime, and brutal punishments of England's past. Unfortunately the Chamber of Terror, as it was called, officially closed in 2016 permanently and was replaced with a wax Sherlock Holmes exhibit.
If they wanted to include Waxwork into the story, than the easiest would be to have her operate something like the tombs in the Labyrinth of Amala in Nocturne, she could make wax figures of previous bosses and challenge the player to defeat them all over again, which would be a great way to allow include Waxwork with the origins of her as a concept in mind. This would also work with the already established canon as Waxwork is in the Undead race in both of her appearances.