Everyone actually in KLK who knows Ryuko seems to be a Ryuketsu. Like Mikisugi's whole stock in the show is that if Ryuko and Senketsu's relationship is true, Kinue gets proven right.
One thing that I’ve always loved about Kill la Kill is that Ryuko and Senketsu have this relationship that’s supposed to be impossible, yet they prove everyone wrong. By the end, Satsuki–who had once deemed their friendship a “fairytale”–completely supports them. Even Tsumugu smiles when Ryuko and Senketsu get back together after Ryuko forcibly tears Junketsu off. In fact, just about the entire (heroic) cast is rooting for them by this point, and are overjoyed to see them working together again:
But more importantly here, I love your mention of Aikuro, because I find him such a deeply fascinating character.
At its heart, Kill la Kill is a story absolutely driven by personal motives. Satsuki wants to stop Ragyo not only to save the world, but to avenge her “dead” younger sister and father. The Elite Four–particularly Gamagoori–are also invested in the greater good, but the root of their willingness to fight is their loyalty to Satsuki. Ryuko, too, enters the narrative not looking to be a superhero, but to learn more about her dad.
So there’s this good moment early on where Ryuko questions Aikuro’s intentions. How does he know what he knows, and why? He’s honestly one of the biggest mysteries the show has to give you initially–he clearly has information, but he’s dragging his feet on giving it out. Still, he answers Ryuko when she questions why. He’s doing what he does to save the planet from the Kiryuin’s tyranny.
I don’t doubt this is true. But I also don’t believe it’s anywhere near the full story. While he may have gotten into the whole Nudist Beach business for such a broad reason at first, his insistence and determination to keep going with it seems to point to something more deeply personal. After all, he doesn’t even seem to know Ryuko, so why is he so concerned for her plight? Why does he fuss over her and want her to succeed with Senketsu so badly, while his coworker Tsumugu wants the complete opposite?
In episode 5, we learn that Tsumugu is–as is fitting for the show–motivated by personal reasons. And as it turns out, extra materials provide some detail for Aikuro’s own motives, too. He was once some cocky, stuck-up scientist, but then he meets Kinue, Tsumugu’s sister, who must’ve been one heck of a woman. She lightens him up and he learns to have fun with life; somewhere along the way, the two become romantically involved and even get engaged. But… then she dies horrifically in one of their work experiments.
So once we get to the series proper, we have these two characters–Tsumugu and Aikuro–who both have lost someone very dear to them, but handle this loss incredibly differently. Tsumugu finds his sister a fool, and everything she believed in stupid and worthless. Aikuro, conversely, follows through with Kinue’s will. Her dying words were to keep going with the Kamui experiments, which Isshin/Soichiro does, ultimately creating Senketsu. Considering how he writes a letter to Aikuro to introduce Ryuko to Senketsu, he seemed to know he wouldn’t be able to do it himself… which puts Aikuro in an interesting place. Instead of orchestrating Ryuko and Senketsu’s meeting, Aikuro could have destroyed Senketsu on the spot. This is surely what Tsumugu would have done. But he doesn’t.
I almost think Aikuro’s role in the show gets overlooked a lot. Literally none of it would have happened if he hadn’t opened up the trap door. Ryuko was in the right place at the right time, but there’s practically no way she would have met Senketsu if someone else hadn’t planned it. I find it pretty interesting that the English dub seems to draw a bit more emphasis on this than the original script, though it’s a recurring element in both. Aikuro is incredibly dedicated to bringing Ryuko and Senketsu together, and maintaining that they stay that way.
And I do think it’s for Kinue as you say, Anon. Aikuro notes in episode 5 that Kinue believed humans and clothes could be friends, so Ryuko and Senketsu are the ultimate way to prove it. Senketsu is the final result of the experiments that Kinue died testing, and instead of believing it’s all hopeless as Tsumugu does, I say that Aikuro chooses to believe in her and her dream. To get more headcanon-y, I think there’s also a compelling thread here about Ryuko resembling Kinue in some way, which just adds to Aikuro’s desire to help her. After all, in the third Drama CD, Tsumugu notes that Aikuro “favor[s] Matoi and support[s] her too much,” and, well, I don’t know about anyone else, but my mind instantly goes to angst-land about how Ryuko looks like Aikuro’s dead fiancé…
Regardless, Aikuro is one of the few characters to regard Senketsu’s humanity at all, and probably the only one who supports Ryuko and Senketsu’s relationship the whole way through. And why wouldn’t he, when that relationship is the living embodiment of everything his lover fought for?