Well hello again :) Thank you for your questions!
Nephrite and Kunzite… oh boy. Do you have an hour? Well, let’s start by looking at the facts. (And by facts I mean 90s-anime-canon with a light sprinkling of manga; the Crystal Shitennou are completely different characters inhabiting a completely different storyline, on which I will not comment save to purse my lips in a disapproving moue.) We never see Nephrite and Kunzite interacting in the anime, and I think this is deliberate. Each is wary and keeps his distance from the other; Kunzite speaks of Nephrite as an unknown and possibly dangerous substance that needs to be tested, measured, and then diffused (which he does, via Zoisite), while Nephrite seems convinced that Kunzite has malign intentions toward him and is spying on him (which he is, via Zoisite). It could be that we’re witnessing the real power struggle within the Shitennou; Zoisite and Nephrite have professional and personality differences that take an ugly turn, but I doubt they would have turned half as ugly had Kunzite not been giving Zoisite counsel. And one can definitely see why Kunzite would want Nephrite gone, and why Nephrite seems genuinely mistrustful of Kunzite’s intentions. Simply put, they’re too closely matched. Both are of high rank (Kunzite a sliver higher, but Nephrite likely not far below), both are very powerful and possessed of esoteric magical knowledge (Nephrite with his astromancy and divination, Kunzite with his multiple dimensions), and though Kunzite may be nominally in charge of the Four, Nephrite makes it clear that he will have no master. One of them has to go.
All of this we can glean by reading the subtitles. But there’s a lot more that we can read between the lines. I don’t have any Nephrite v. Kunzite headcanons as fleshed-out as I do for Zoisite and Kunzite, but I’ve been having a lot of really wonderful conversations with whereyoursoulresides lately, and her understanding of the nuances of Japanese has offered some fabulous insight onto the Shitennou as characters, which in turn might tell us a few things about why they behave the way they do. For example, did you know that Nephrite and Kunzite talk differently? That Kunzite’s speech patterns, use of pronouns, etc, is a couple of decades behind Nephrite’s? Now that’s an odd thing, don’t you think? Is it a generational rift: the result of an age difference between them? Or does it say something about each character’s origins and identity, and how each imagines himself?
Nephrite is very much a modern man: his idioms are current (or at least 90s-current), his wardrobe epitomizes the height of fashion (dig that collarless shirt), and his playboy persona suggests that he fancies himself not merely an elite soldier but also a member of elite society. An aristocrat, in other words: born to do as he pleases, both above ground and below. Now contrast this with Kunzite. Here you have a man who puts on no airs and cultivates no social charm. He has no civilian disguises, no contemporary alter egos. He appears in the modern, surface world only when he needs to, usually with the aim of plunging it into pre-electric darkness. His speech is uncultured and brimming with antiquated machismo. The pronouns he uses to refer to himself and to Zoisite are out-of-date (even by 90s standards) as well as a trifle lowbrow; unlike suave, worldly Nephrite, Kunzite’s a relic of the tough, stoic “ore”-male stereotype common in early anime and manga. Behind the times and sorely lacking in sophistication– essentially, he’s a troglodyte. (A very smart and eccentric troglodyte, which is why I love him. But I digress.)
… All of this is to say that I wonder if there’s not a bit of class tension at the heart of Nephrite’s and Kunzite’s cold war. It’s going out on a limb, to be sure, but the difference between these two characters’ comportment suggests that the two are very different kinds of men: one a goldfingered metrosexual who believes the best way to triumph over modern society is to beat it at its own game, the other an old-fashioned soldier, likely of low-to-middling origins, who has little patience for airs and graces and probably isn’t aware that it’s no longer cool to openly comment on the quality of a woman’s “gams.” Imagine how mistrustful each must be of the other; highfalutin’ Nephrite would resent someone like Kunzite – basically a thug, and a queer thug to boot – outranking him, while Kunzite would be wary of Nephrite’s seemingly effortless ability to infiltrate the modern world and bend it to his will. Each embodies a different vision of how the Dark Kingdom ought to operate, so it’s no wonder each wants the other out of the picture.
So much for Nephrite and Kunzite. Nephrite and Jadeite? Zero readings there, I’m afraid; I can’t even imagine what they would talk about in the mess hall, if they’d talk at all. Anime and manga canon conflict on the matter of Jadeite and Zoisite; the former would suggest Zoisite has nothing but contempt for Jadeite, while the latter offers the tantalizing notion that the two were close enough friends for Zoisite to take personal revenge for Jadeite’s death. I love this idea, but it doesn’t square very well with the version of the Shitennou that I know best. So I hedge my bets and imagine them as fellow misfits, one queer as a clockwork orange and the other an introvert whose awkwardness gets misread as arrogance, each unconsciously sympathizing with the other but not shedding any tears when the other takes a fall.
Though in a pinch I will speak up on Jadeite’s behalf, particularly regarding his relationship with women. I know it’s fashionable to decry 90s-anime-Jadeite as a woman-hater, but in all honesty what most people read as misogyny comes across to me either as garden-variety, old-fashioned male chauvinism (likely quite common in the time and place Jadeite hails from) – or, if we want to take the Jadeite-loves-Queen-Beryl route, contempt for any woman who is not his queen. The aspersions Jadeite casts on the female sex have to do with weakness, helplessness, and clinging. However, this may be less a comment on the frailties of womankind as a whole than a reproach he levels at particular women for exhibiting behaviour he deems unworthy or below them. Which stands to reason, if the woman he idolizes wields absolute power and answers to no one. So Jadeite loves Beryl? Sure, why not. Is the love requited? I highly doubt it.
Phew! I hope that answers your questions and you don’t regret asking them!