The game makes it quite clear that Sho is just a whiny little emo-child, who craves for someone's arms to hold him tight. His constant chatter on friendship and bonds and how much he hates both, only serve to pinpoint the obvious need for attention -- The funny thing is that in regards to reducing Persona 3 & 4 to a caricature of itself along with its characters, reducing it to nothing more but jarring lessons in the importance of friendships and bonds.. Sho is the character who keeps banging on about it all the most. In other words; He's like your average anime villain, whose backstory and motivations are so incredibly shallow and cartoonish that it's physically painful to behold.
Sho is supposedly meant to be portrayed as the opposite spectrum to Narukami, but developers failed to remember Adachi already served that role. He also had the advantage of having a connection to Yu -- Adachi chose to neglect social affairs and ended up being rejected when his hard work meant nothing. Ultimately, he gives up on everything. He's a void of a man that acts without conscience or reason, where Yu acts as a listener, uplifter and utilizes his natural talents to help those around him, thus letting them spill the truth about themselves so that they may come to terms with it. Adachi, however, abuses his power to do what he like, just like how he became a cop for the sake of a gun license, and he believes 100 % in his own image of a broken world, where only the previliged may succeed-- Sho's motivations doesn't reflect anything the cast fights to believe, he shuns the world despite the fact that he doesn't really believe in any of the stuff he do. There's no conviction, no real motive, just a bunch of whining and self-loathing.
The comparison to Izanami and Nyx is a bit odd, considering either aren't really much of an entity as they are a concept. Nyx is but an abstract personafication of Death, the subconcious desire for one's demise (Freud referred to it as the Death Drive), where her existence is to solely to carry that out. It's what made both Izanami and Nyx frightening, the idea that humanity's subconcious desire for self-destruction, leads to the creation of a monstrous two-headed dog-looking monster, Erebus, with the purpose of ending everything is very much terrifying.
The same can be said of Izanami. Ultimately, she was an observer, who chose to test humanity in a gamble, as to determine whether or not they'd be able to accept their flaws as humans and live with them, or they'd choose to live a lie for the sake of keeping face. As in myth, Izanagi was horrified at seeing Izanami's "true" monstrous form after her death. He ran from the cave and blocked off the entrance. In Persona 4, the myth serves as a metaphor for the refusal to acknowledge complete truth. Izanagi refused to accept his wife's new form, and blocked himself off from seeing it. In turn Izanami was left stuck in the darkness, eventually assuming that the "truth" of the matter was that people suck and are jerks and were all shadows at heart. Two halves of creation refuse to acknowledge each other, acting as an Original Sin of sorts for the game to build upon.
It comes out of their idea that people are an extension of each other, we don't really believe the things we do or things we acknowledge, we just do it at the expense of the other guy so they'll notice you. We all have some terrible qualities about ourselves, but it's part of us and it doesn't necessarily represents the whole, but we rarely notice that. We are cardboard cut-outs of each other.
Ultimately though -- Neither Nyx or Izanami really wanted humanity to fail. Nyx wanted humanity to accept life's grandeur and overcome the thoughts of preventing something that can't be changed and instead choose to accept it for being a smaller piece of the whole, while Izanami wanted people to accept each other for who they are, be themselves and express it to the world instead of cutting corners.
What makes them fascinating is this sense of duality and how they aren't necessarily good or evil, they are just constructs born from humanity itself, a sort of limbo-realm-figure who exist less as a hindrance and more as a neutral party guidance of some description.
Takaya, while not being incredibly interesting, at least served a meaningful purpose in the narrative. He represented that part of humanity that seemingly embraces the desire of extinction -- he's the other side of the spectrum, who welcomes the end with nothing to lose. But that's where the paradox lies -- He choses to accept death, though because his life is on a short timer he denies the any sense of joy in living and without the fear of death then ultimately he hasn't really accepted the inevitable and the important fact that Death and Living aren't mutually exclusive. It's part of the journey that is life, and once you finally realize that and when you get there, you'll come to appreciate what you've experienced and cherised, but he rejects this. He is a dying man, and rationalizes that since he cannot live life, there is no point in anyone else doing so either. The Fall is his salvation; all he wishes is to see the end of all things before he perishes. This is why he contributes to Nyx's coming.
In fact, much like Adachi's reflection to the protagonist of P4, you can easily distinquish certain parralels between Takaya and the protagonist of Persona 3.
Takaya clearly mimics Jesus Christ. But there is something very off about Takaya and his persona; they look really pale and sick. Minato/Minako and Takaya are a bit like twins, just like Thanatos and Hypnos. Takaya is a false saviour and represents nihilism, death and destruction, whereas Minato/Minako is a true saviour and represents faith, life and creation. Takaya sacrifices others for himself; Minato sacrifices himself for others.
Sho has none of these qualities -- He's characterized as no less but a dumb punk kid who doesn't know any better and doesn't even have anything to believe in. He willingly places himself in the service of a retarded god thing (Kagatsuchi being the most out-of-place villain with the Persona lore), he's then granted inexplicable powers to control people's minds, because why not? He uses this whack power to even freeze some of the heroes in place during the story because he can -- But he doesn't kill them, even if he was granted about 10 different opportunities to do so all the time, despite the fact that he's been blabbering on about how he wishes to rid the world of everyone except himself. Then at the end he acts all "surprised" over the fact that the ominous spawn of the cosmic netherrealm chooses to betray him, when anyone with a brain cell could have figured that out. It is then later on revealed that he was also apparently, for some reason, present during the exact dates of events when the fog took over Inaba and witness the whole debacle with Adachi -- This is such an unprecedented train wreck that it almost feels like it could have been written by the guy who made Bleach, where the villains and protagonist all pull out incomprehensible deux-machinas or hidden knowlegde/connections/revealtions (until now) to grant either or an edge over the other party, and to clumsily tie plot threads together, in a bad attempt for dramatic effect. There's also the big inconsistency with Persona 4 Arena, where the Eerie voice went on about how he wasn't able to "enter a TV" since he doesn't have a Persona, which only screams of bad writing and continuity errors, when he quite clearly does. The Eerie voice mannerisms suits the personality that carries a Persona, not the one that doesn't. I could also go into what it is that makes Kagatsuchi so incredibly terrible but I'm sure there's no need.
Sho isn't any better or worse than him -- He shouldn't be celebrated for living up to how the terrible writing presented him as, being a ****** who just needs a hug. That's not what I'd classify as "well written" -- Deliberately making a character annoying is still annoying. Sho is as terribly written as Kagatsuchi, with the saving grace of being voiced by a great voice actor. That's it.