Spoilers!

TL;DR: Diebuster is a bold announcement by Gainax that being Topless is the direction Gainax is headed. Making this a sequel to Gunbuster is the clearest and most gratuitious way possible to announce that it's time for out with the old, and in with the new. Does that make me like Diebuster more? No; it's a strange show that stands on shaky legs on its own and completely falls apart burdened by the legacy of Gunbuster, but on some level, I do get it.

If you appreciated Gunbuster and its conclusive ending, pass on this. If you've never watched Gunbuster though, there are certainly worse shows to spend 6 episodes on. Mostly only recommended for Gainax enthusiasts. The aesthetic and design might appeal to fans of FLCL.

My feelings on Diebuster are much more complex than that of Gunbuster; whereas Gunbuster was admittedly difficult to ingest but very stunning when reflected on and taken as a whole, Diebuster is nonsensical and banal enough to take in easily but leaves little to look back on, comprised of several good parts mixed in with many, many things that don't really add up to a satisfying sequel.

I think the primary reason for this is that Gunbuster is a fascinating product of experimentation with the mecha genre as a whole, whereas Diebuster is really only a step forward for Gainax itself. In Diebuster you can clearly see how Gainax's approach to mecha anime has evolved since Gunbuster and Evangelion and begun to take on the shape it would use for Gurren Lagann, but I think the issue is that the middle-ground in this transitionary phase really just isn't as satisfying as either. It doesn't have as much of Gunbuster's rigorously detailed science fiction and avant-garde psychological aspects, nor does it have the same caliber of absurd, laws-of-the-universe-defying power of Gurren Lagann. This show marks the transition from the experimental, thoughtful, and grounded to the inspiringly heartful and gratuitous, but doesn't really succeed at drawing me in with either.

I think that having Diebuster be a sequel to Gunbuster makes sense in terms of Gainax's history, but does a disservice to Diebuster, which I think I would enjoy more as its own property. Case and point, the only part of this show that actually struck me at any emotional level was the finale wherein we see Gunbuster's return home from Lal'C's perspective. I can't help but feel that Noriko and Kazumi would be disappointed to find humanity in the state its in: resigned to its own solar system, technologically regressed, seemingly devoid of the spirit of progress and survival they fought for, and somehow much more vulnerable and cowardly than the comparatively stubborn warrior-race they hail from. Diebuster mostly only feels like a sequel to Gunbuster in the few moments where nods or references to Gunbuster are included.

With Gunbuster, I really enjoyed how clear it was that incredible amounts of attention to detail were given to the fictional scientific principles, as well as how much effort was put in to make sure these principles were enacted consistently, such as how they made it clear how that various characters were travelling through time at different rates, which of course becomes essential to a lot of the character development and the finale. The cute Gunbuster science lesson shorts are great evidence of this detail. While Diebuster's science lessons also attempt to infuse the phenomena in the show with scientific jargon, it still stands that the Topless powers and the strange-looking Buster Machines just don't feel right in the Gunbuster universe. Annoyingly, I think that Diebuster still gets away with this by placing the show 12,000 years after Gunbuster; in that vast span of time it's entirely conceivable that humanity developed strange new technologies that are unrecognizably different than those used during Gunbuster. Still, it bugs me. Alongside the complete absence of comprehensible reference to the passage of time despite travel all throughout the solar system, Diebuster didn't impress me as much as Gunbuster in this specific aspect.

Only a few new things in this show make any amount of sense when applied retroactively. As annoying as it is that Topless powers barely fit with the universe, it is possible that Noriko and Kazumi possessed some version of this power that made them the chosen pilots for Gunbuster despite Noriko's obvious shortcomings and the greater skill of many of her fellow pilots. Perhaps a little-known fact, we do also have hints of supernatural powers referenced in the Gunbuster science lessons, as the powers of "ESPers" were required for the highly advanced travel systems of the flagship used in the Gunbuster finale, so Topless powers aren't entirely outside the scope of Gunbuster's canon. Humanity's abandonment of degeneracy technology, warp capability, and technological progress in favor of hiding in their solar system also closes an obvious question from Gunbuster, namely, why wasn't humanity capable of recovering the Gunbuster crew with 12,000 years to prepare? Wouldn't technological progress have developed sufficiently to do so? The answer, apparently, is no.

The most enjoyable part of this whole show by far is Nono herself. Goofy, earnest, kind, and full of hard work and guts, her enthusiastic personality and animation are a joy to watch when contrasted with the dull characters she's surrounded by. Her zeal for life and heroism are great fun, but that positivity is basically all squandered because she spends the whole show getting put down and abused by the people around her. Literally not until the moment before she's gobbled up by a singularity does Lal'C, much less anyone else, finally treat as an equal rather than discarding her without hesitation to pursue their own selfish goals. Nono is the embodiment of the spirit and resolve that Noriko fought to attain in Gunbuster, and pretty much no one else in this show even comes close to truly understanding that or earning the right to follow in Noriko's footsteps. Her bartender boss puts down her dreams; the very first robot pilots we see at the bar essentially sexually assault her; Lal'C brushes Nono's admiration and attempts at friendship off and treats her likes shit; Tycho spends her whole episode (why did she get an episode to herself, by the way?) being a douche because she sees Nono as an inferior rival for the right to pilot the new Buster, and even after Nono gives her a pep talk that helps her leave her hang-ups behind and awaken the Buster, she seemingly reverts to ignoring Nono for the rest of the show instead of being supportive; Nicola tries to rape her (then gets to join the army after for some reason, like no one cares that he did that?); Casio peeps on her in the shower like a pervert then subsequently casts her goals aside on Pluto in order to follow his selfish and vain mission to become a Topless Buster pilot again; and pretty much all of the other essentially irrelevant characters in the show generally just treat her like garbage until she ends up being the apparent savior of humanity. For as loveable as they made Nono, she really got the short end of the stick, and it isn't fun to watch. It's not even like anyone had a valid personal reason to be dicks either; just greed, immaturity, and downright evil. People were rude to Noriko too, but at least she worked out those dramatic tensions with people and got a happy ending. Nono got the short end from tragic start to tragic finish.

It does warm my heart though that Nono is the byproduct of a much earlier, more hopeful humanity's reverence for Noriko, clearly designed to be the Gunbuster crew's heroic and spirited successor. Seeing as how Nono is Buster Machine #7, and the latest model used in Gunbuster was #3, it's likely she was created not long after the battle at the core. It's just a shame that she ends up being such an outcast. I like to imagine that they also designed a Buster after Kazumi.

Of the few things in this show I genuinely appreciated besides Nono, I did enjoy how the regression of humanity is made palpable by making the original Gunbuster space monsters incomprehensibly powerful and practically indestructible by comparison, to the point that humanity barely stands a chance against one of the things, much less the tens of billions faced in Gunbuster. Didn't really care for their ugly screaming sound effect, but that's a minor point. I do find it a strange choice for a sequel, however, that humanity faces a much, much weaker enemy instead of a more threatening one.

Finally, I do appreciate how the whole premise of being Topless is just a big, hilarious reference to Noriko tearing her shirt off in the Gunbuster finale in the moment she removes Gunbuster's first degeneracy generator to activate the blackhole bomb. From the name alone, it's very clear what sort of principles being Topless is really meant to embody: namely, that Gainax absolutely loves making girls rip their clothes off when they power up. In this regard, I think it makes sense to consider Diebuster to be a bold announcement by Gainax that being Topless is the direction Gainax is headed: "yeah, this is nothing like Gunbuster, but it's what we want our future to look like, so we hope you stick around to see it." Making this a sequel to Gunbuster is the clearest and most gratuitious way possible to announce that it's time for out with the old, and in with the new. Does that make me like Diebuster more? No, but on some level, I do get it.