Why are Goku Uniforms marked with stars? To denote the percentage of extraterrestrial material.
How did Maiko get a cast on her arm if she only was injured shortly before? She wasn't injured in the first place and had the cast the entire time, waiting for an opportunity to garner sympathy and join Ryuko and Mako.
This is foreshadowed by her using her "injured" arm to drive the bus.
Senketsu finding Maiko's blood to "taste disgusting" becomes a lot more interesting after we find out he was made to be worn specifically by Ryuko. It could be that any blood that isn't hers tastes disgusting to him.
Alternatively, it's like trying to give someone a blood transfusion with a blood type that doesn't match their own.
Also, the fact that Satsuki is able to wear Senketsu with relatively little trouble (though she can't hear him talk , at least initially anyway) probably has something to do with them being sisters, and presumably having extremely similar blood.
Ira Gamagoori's power-up is in a BDSM getup that get more power as it gets attacked. It might psych people out at first, but it has to be remembered what his role in the academy is, which is the Disciplinary Committee Chair. What is one of the main focuses in BDSM culture?
In addition, his counterattack-based style also plays into this. You can't enforce the rules unless they're broken.
Lots of it with Mako's 2-Star Uniform. Let's see...besides fulfilling a disparate symbols of delinquincy, besides being 'Mako underneath'...besides being a shout-out to Jotaro. Why is it so messy? Mako-chan is not only conflicted with HERSELF, but it was also a last-minute uniform for a club that wasn't prepared.
The anime is about a teenage girl who goes through changes that requires bleeding to activate, and is initially having trouble coping with these changes because she is self concious about people looking at her body. Just like Tengen Toppa Gurren Lagaan could be seen as a boy's anime about reaching adulthood, Kill la Kill is a story about a girl climbing through adolescence.
Going further with that, in the ending she is shown to be somewhat in conflict about the fact that she can no longer wear her sailor uniform, something that signifies her inability to come back to what was before as she climbs through it and no doubt something she isn't the only person to feel.
Satsuki's "Pigs Wearing Human Clothing" comment becomes a lot more poignant after what we see in Episode 7, seeing Mako and her family being seduced and corrupted by the power and prestige of their new position. Chances are, the exact same thing happened with all the other club captains. It's implied that Satsuki considers conviction and strength of character to be the highest of virtues, so why wouldn't she look down with contempt on those who abandoned any ideals or principles just to hold on to power and wealth? It also explains why she smiles when Mako gives up her position (aside from the completion of a Xanatos Gambit). Mako abandoned her wealth and position in favor of loyalty to her friend (probably the first time that's ever happened), meaning that she's likely earned Satsuki's respect.
The concept of Life Fibers might have originated from Panty & Stocking with Garterbelt, a previous show from the same director and staff. Both shows have transformation sequences where pieces of clothing are changed into weapons.
At first, it seems strange that the order of battle for the Elite four is goes from the one who defeated the least amount of student to the who who beat the most, until you realise that Satsuki was enforcing the Sorting Algorithm of Evil to train Ryuko.
Sanageyama leaves the arena as soon as Nonon is called to battle. Sanageyama complained to Satsuki in episode 6 that he's developed hypersensitivity of his remaining senses after giving up his eyes. Nonon's fighting style and Uniform abilities are based on incredibly bombastic music attacks, and she even enters the arena with a loud marching fanfare. Sanageyama was trying to spare his ears from over-stimulation.
Part of above, but when Ryuko challenges all of the Elite Four at once they decline in favor of one-on-one battles. While powerful alone, all of their abilities would have stepped on each other's toes and done more harm than good. Along with the Jakuzure/Sanageyama example above, Inumuta has been shown to have a weakness to wide area-of-effect skills and couldn't calculate Ryuko's actions and dodge the crazy flaying of Gamagoori's whips at the same time. Jakuzure would probably kill everyone with her missiles as well.
Also a part of the example above, if you pay attention, you might notice that Sanageyama came back during the Jakuzure fight but only after her first form got defeated. He came back because he knew that the sound coming from Jakuzure's Da Capo form would be focused only on Ryuko.
Sanageyama jobbing to Nui actually makes perfect sense in retrospect. The target fought him by waiting until he was overcommitted to an attack, hitting a weak spot he didn't know about, and the target was apparently unarmed. Even "The Eyes of the World" cannot protect against something that is not of this world.
In her flashbacks, Ryuko's memory of her father's killer slowly changes to resemble someone who looks like Satsuki (before being revealed as Nui Harime). In other words, Ryuko's becoming obsessed with Satsuki to the point where she might be convinced that she was the one who killed her father. It becomes even more brilliant when you go back to her first flashback in episode 1 and realize that originally the silhouette of the killer had twin pigtails just like Harime.
The other half of the scissors blade that Harime possesses at first doesn't seem to match up to Ryuko's half. That is until you realize that both halves combine to form a pair of sewing scissors◊.
The things that Ryuko and Satsuki say after their Transformation Sequence differ greatly as a reflection of their relationship with their Kamui. To elaborate, Ryuko says "Life Fiber Synchronize", indicating that she and Senketsu move as one, while Satsuki says "Life Fiber Override", explicitly stating that she is Junketsu's master. This also speaks of their mastery of their Kamui, as Ryuko and Senketsu have a chance of going berserk if one of them is out of sync, while Satsuki is always confident that she is in control of Junketsu's power. Satsuki also needs to be always in control of Junketsu, otherwise, she would've been devoured if she lost control.
"Before My Body Is Dry", either lyrical or instrumental, normally plays when Ryuko and Senketsu are in sync with each other which makes it seem like a normal insert song. Not really though, as it's revealed in the OST that there are two singers in that song, one female and one male. And the lyrics pretty much describe the relationship between the two. Seems like they are not fully in sync yet, as we have yet to go pass the part where the woman is done singing and the next verse begins, sorta like how Ryuko does not always heed what Senketsu tries to tell her. Like when her rage taking over and corrupting him causing the transformation to become monstrous.
Why would Nagita, the News Club President, be hiding in a cubicle and waiting for Mako in the girls' toilet of all places, even if he was really desperate? Well he wasn't ever really a he was he?
Normally the three drunks from episode 6 having pictures of Aikuro and Tsumugu together could be dismissed as just something funny. But what if they were actually Kiryuin spies, or just someone who was paid for the information? Aikuro saying that "Kiryuins have no eyes here" seems like classic Tempting Fate and episode 15 proves that Satsuki knew about Aikuro being a member of Nudist Beach. It might have been his meeting with Tsumugu that gave him away.
It wasn't. She knew even before that, but pretended not to for various reasons.
Throughout the series, Satsuki has called people "pigs in human clothing". Come Episode 16, we see that the Life Fiber aliens view humans as livestock.
Ragyo's speech about how "clothing is original sin" and relating it to man becoming aware of his nakedness by eating from the Tree of Knowledge gains a much deeper meaning after episode 16, where it's revealed that it's the Life Fibers themselves that made mankind wear clothing and allowed them to evolve as the dominant species on the planet.
Tsumugu sometimes mentions not minding being a naked nudist if it will let him continue his quest of destroying all Life Fibers. The statement itself seems odd coming from a member of a nudist organization, until you realize that he's the only Nudist Beach operative who actually wears clothes while working (Aikuro doesn't count since he's undercover). Those clothes apparently let him store and carry all his gear, from his needle guns to his bombs. Also, as shown in episode 15, low ranking members of Nudist Beach (again, with the exception of Aikuro, who is implied to be the acting commander) wear almost nothing but utility belts, so to Tsumugu, being a "naked" nudist essentially means being stripped of all his specialized gear, and possibly being demoted to a lower rank.
Later on we find out that Tsumugu is only a nudist out of Practicality/the need to defeat the Life Fibers. In the End, he asks if they can finally put clothes on now, while Aikuro actually enjoys being a nudist.
In episode 18 when Ragyo takes Satsuki's Junketsu from her, she touches her daughter's crotch to rob her of her "purity".
It had been implied earlier that Satsuki had some special reason for leaving the Kansai region last in her plan to conquer all the schools in the country, but episodes 14 and 15 didn't really dwell into this reason very much. After episode 17 it makes perfect sense, as she knew that Nudist Beach had their base of operations somewhere in the region and wanted to give them ample time to prepare and dig in, so that when she would be required to confront them they could anticipate her actions and preserve a portion of their forces for the future, thus allowing them to remain potential allies when she executed her Heel-Face Turn. A masterful Xanatos Gambit if there ever was one.
Ragyo is in perpetual Super Mode. Up until Episode 18 her hair seemed more of an aesthetic kind of thing or a way to show just how inhuman she is. But then we see Ryuko activating her own Super Mode and her hair shines the same way as Ragyo's. The power up which allowed Ryuko to completely outperform Nui, Ragyo was using from her very first appearance.
Tsumugu's attitude towards Ryuko makes more sense if he knows that Ragyo is actually Ryuko's mother, since he has more than ample reason to distrust the former.
The streak in Ryuko's hair is a side effect of being infused with Life Fibers, which are also red. Remember, when she broke free from Ragyo's mind control, it was her hair streak that cut the bonds on her brain.
The One-Stars of Honnouji Academy lack any individuality and are basically clones of each other. It can be seen as biting commentary on the mundane middle class. Or de-individuation that gets drilled into soldiers at boot camp, with Honnouji Academy being the camp.
When Ryuko went berserk, she transformed with Senketsu, becoming a powerful and bloody monstrosity instead of clothing like victims of Kamui's should. One might say this is because she's wearing Senketsu, a sentient Kamui, but it's actually because Ryuko is a human-Life Fiber hybrid and because of that, her body is capable of transforming or combining with other Life Fibers like Senketsu.
She's also the only one who can hear Senketsu's voice, which at first, seemed only because according to Aikuro, her DNA has been spliced with Senketsu. After the reveal of her being a human-life fiber hybrid, it makes more sense why only she can hear and likewise communicate with Senketsu, a fully sentient life fiber being.
It's curious that Ragyo also uses Life Fiber Override while wearing Junketsu, considering that she's a loyal servant of the Life Fibers and shouldn't need to force them to cooperate with their mutual goal. A hint that Junketsu might be more like Senketsu than we realise, perhaps?
Or perhaps it is just the opposite. We haven't seen any other Kamui to compare them to, but we have to assume that Junketsu is a typical Kamui and thus has to be forced to cooperate (hence the override). Meanwhile, Ryuko has some Life Fiber inside of herself and Senketsu was spliced with her genetic material when it was being created, which pretty much means that Senketsu is half-Ryuko (hence the synchronization).
In addition, it should be noted that, while Ragyo is a servant to the Life Fiber species in general, she still tends to order them around. See: Shinra-Koketsu's Absolute Domination. She does not have a bond of trust with Junketsu. Even though it can't consume her, she's still giving it commands like a general would to a soldier.
Nui actually saved Ragyo's life when she distracted Ryuko in the 18th episode. If Satsuki and Ryuko were allowed to go after Ragyo together then it's very likely that even though Bakuzan was not able to kill Ragyo, Ryuko could have followed up with her Scissor Blade which, as Matoi Isshin put it, can cut the life of life fiber.
Unfortunately not. Life fibers must be severed from both ends as though they've been cut with a scissor if they must be stopped from regenerating. If Satsuki had known, she could have asked Ryuko to cut Ragyo's head off from the other end, but that was no longer a possibility with Bakuzan broken and Satsuki thrashed.
Every time a character has had their uniform destroyed, they've been 'stripped' completely naked, with three notable exceptions: Mako, Ryuko and Satsuki. Instead of being stripped naked, all three kept their underwear on, meaning that while they may have lost their clothes, none were 'stripped' of the will to fight.
Takarada's Giant Enemy Crab robot requires its pilot to be in the same position as the DTR. It's not a coincidence - Takarada Conglomerates has just been confirmed as a monetary supporter of Nudist Beach. They're probably using some of the same specs.
For a while, due to his red hair and general attitude being similar to the protagonist, we thought that Tsumugu was related to Ryuko. He was a red hairing
For a while it seems sort of hypocritical for Satsuki to reinstate the Elite Four even though they lost to Ryuko in the Naturals Election. Then you realize that she has four positions that need to be filled and, despite their loss to Ryuko, they're still the most eligible students, especially considering that Ryuko was refusing to go to school (let alone accept a position).
Assuming that the show really is trying to address the gender roles applied to girls, Ryuko's Mind Rape in Episode 20 takes on a whole new meaning. She has never had a Love Interest, or claimed to want/need one, being more or less completely independent and focused on revenge and world-saving. However, the Fake Memories Ragyo shows her include a scene of Ryuko getting married, a traditionally "acceptable" dream for a girl to aspire to - in other words Ragyo is trying to force Ryuko to adhere to female stereotypes, first as a dutiful daughter and then as a blushing bride.
On the other hand, we cannot say for sure that it is something Ryuko does not want. Yes, she is a not-so-feminine delinquent, but she only became like that due to living away from her parents and trying to protect herself from being picked on. It might be that she wanted to live a life of that sort, but couldn't due to her circumstances and convinced herself she doesn't care in order to not feel pain.
It didn't seem so much that Ragyo was forcing Ryuko into that stereotype as she was brainwashing her with it, which gives an entirely different message. Ryuko has been denied nearly all forms of happiness her whole life, and only knows what it looks like from the outside. Ragyo was convincing her that being independent and strong had brought her nothing but pain and betrayal, and she'd be much happier submitting to traditional values.And it worked.
Then again, considering that Ryuko could not "submit to traditional values" in the past and she suffered because of that, who is to say that she doesn't want to submit to them, or rather, that she would naturally be that way even without submitting to them had she been allowed to live her life the way she wanted to? Maybe ... just maybe. We don't really know. It could be that the Fake Memories were of a world where she submitted to "traditional female values", but it could also be that they simply were of a world where she lived with a parent and didn't have to fight and this made those Fake Memories into what we saw.
There might be a reason why Ryuko can survive so much blood loss other than just stylism or symbolism. Other Life Fiber hybrids are able to shrug off both damage and blood loss pretty well. For example, when impaled, Nui lets out a huge jet of blood and has the requisite Blood from the Mouth for a few seconds, then instantly flashes to perfectly fine as soon as she stops pretending to be mortally wounded. Blood loss would eventually incapacitate or kill Ryuko, but she has a much higher tolerance than normal people.
As much as it might seem like a retroactive justification, the reason why Kamui tend to be skimpy because less surface area makes for less mind control makes a lot of sense. Life Fibers feed off human neuroelectric signals, so they interact with nerves. The less skin the Kamui touches, the less nerve endings the Life Fibers (which Kamui are 100%, after all) come in contact with.
While Satsuki and Ryuko fight, they say that Ryuko isn't wearing Junketsu, instead Junketsu is wearing her. What if, it was really Junketsu insulting Satsuki, saying she's not worthy of wearing him, by using Ryuko as a mouthpiece?
At first it looks like Ryuko exterminating the Club Presidents is detrimental to Satsuki's plans. After all she is destroying her most effective fighters with custom uniforms. Following the revelation from episode 17, however, it all starts to make sense. One-Star students are drilled and molded into being obedient to Satsuki to the point where they have little individuality left. They are essentially foot soldiers with loyalty and discipline crammed into them. Two-Star students, however, are far more individualistic and it's very likely that they follow Satsuki only for personal gain. If Satsuki would go to war with Ragyo with two star students as her officers they might just as well get scared of losing their status and possesions and would rebel against Satsuki and side with Ragyo.
At first we get the impression that Matoi Isshin was not a very good father. He spent most of his time absorbed with his work and sent his daughter Ryuko to boarding schools. Then we find out that he was not only the founder of Nudist Beach but also Ragyo's husband. The Kiryuins probably wanted him dead and assassination was always a possibility. Furthermore, it would not take Ragyo a lot of effort to figure out that Ryuko is her daughter and heaven alone knows what manner of horrors Ryuko would be subjected to then. There was no way he could guarantee Ryuko's safety except by sending her far away.
The beginning of the episode 21 may seem like just another way to show just how depraved Ragyo and Nui are but there is actually more to that. The scene looks like rape for a very good reason, Ragyo and Nui are doing something even worse to Ryuko. They violate both Ryuko's body by grafting Junketsu on her, turning her into nothing more than their toy. But they also violate her mind and soul, rewrite her memories, change her personality. The truth behind the scene is even more horrible than if it would be a normal rape.
The way the Scissor Blades work has caused confusion—Isshin manages to take out one of Nui's eyes, but Nui and Ragyo can regenerate themselves from wounds inflicted by Ryuko's red blade. Episode 22 confirmed something that had been long suspected by fans, and rather obvious in hindsight: Because the blades are two halves of a giant scissor, they kill life fibers only when used as a pair, just like scissors do.
Of course Iori's uniform was a Three-Star Goku Uniform. Most did not notice because he was a club president (all the other ones were two-star students), he never used his uniform, and he used Inumuta's help when sewing that experimental five-star uniform way before all the weird things happened, but one need only compare the style of his uniform to that of the other students. The uniform of every other club president just screamed "custom" whereas his looked similarly to the ones the Elite Four wore.
Also, keep in mind the location of the third star. It's on the lapel of his uniform, which until he transformed was hidden from view. It was always there, just no one could see it.
Another one about Iori's outfit. Notice how he's always wearing what appears to be a breathing mask with filters? It's likely a safety precaution since we know that life fibers are parasitic, it would make sense he doesn't want to inhale/ingest a stray, floating life fiber, which he is likely to be around due to his club - the sewing club. Note that the rest of the sewing club wear similar breathing masks.
Nui's only parental figure was Ragyo but think about this way. Ragyo was the only other Life fiber/human hybrid like herself until she found out Ryuko was one too. Nui's words to Ryuko, about how only she can understand her and her anger towards her after episode 22, takes on a sadder meaning. Despite her insanity, Nui might have just wanted somebody, other than Ragyo, who can understand her pain of being different than everybody else.
So why exactly did Ira have to jump out the window and fall to the ground in episode 1, he could just chase the student down right? Wrong! He couldn't because running in the corridors is against school regulations. So he jumped out the window because that isn't against school regulations.
Why did Mako's two-star fight club uniform disappear at least until episode 22, with no mention of it whatsoever? Rule one of Fight Club!
Erm ... it sounds more like a lame joke rather than Fridge Brilliance. It was destroyed, remade in that episode, and nobody thought they'd see it again until that happened; that's enough of a reason not to talk about it with everything that happened around them.
Her uniform is also the first two star to be reproduced because aside from the explanation that she has the greatest difference in combat abilities in and out of a goku uniform, hers is just a longcoat+hat+geta ensemble, something that Iori can whip out in probably two seconds with his skills.
Kamui needs a blood sacrifice to activate. The ultimate Kamui Shinra-Kōketsu that makes Ragyo look like a goddess needs a human sacrifice.
Why is the new Goku uniforms let the four deva go face to face with Ragyo without getting curbstomped like before? It's because it's based on Senketsu rather than the normal kamui, that explains the black colour and the much less "skin contact".
It's not only that: The Goku uniforms most likely had their life fiber percentage greatly increased, to the point of requiring the reduced skin contact to avoid getting manipulated by the life fibers!
To add on to this, the gradual change in their uniforms also serves to show their alliance. At first, they wore clothing that completely covered them and that were very bulky, bar Inumuta's, which showed that they worked for Ragyo. As they got closer to their change of side, the uniforms slimmed down until we reach their final form, which is very revealing, thus showing their status as true nudists, working against Ragyo.
Adding to the fridge brilliance, that's not the first time they observed Senketsu before upgrading the Goku uniforms. It also happened before the school trip, adding to the notion that they wanted to get as far away from the original kamui so they won't get absorbed.
In episode 24 Ryuko says that she will become more powerful that closers she comes to death. This seems odd and people have been joking about it for awhile now. However it all makes sense when you remember that she and Senketsu just absorbed all goku uniforms, including Gamagoori's uniform which becomes more powerful when attacked.
Why was Ryuko able to call Satsuki "sister" after her fall from space so easily even though they weren't able to form a sisterly bond before and agreed not to try for now? Because of how frantic Satsuki was to catch her and with how she kept Ryuko in her arms after catching her, just like an elder sibling would hold younger ones. For probably the first time since Isshin sent her to a boarding school Ryuko felt safe then, and family aren't those who share your blood, family are those who make you feel safe.
It always bugged me how Iori essentially disappeared during the finale considering how important he was. However in the end it makes sense; he's a club president. And after a president loses their uniform - which he did by letting Ryuko absorb it to power up Senketsu for the final battle against Ragyo - they essentially disappear since they're not needed anymore. Even the other presidents pretty much disappeared in the final scene.
In Japanese culture, cutting/shortening your hair is considered symbolic of casting aside your old life and beginning a new one. Satsuki's new bobcut in the epilogue makes a lot more sense with this knowledge; she has ended her life of pretending to be a fascist despot and has begun the happy life with her sister Ragyo had long denied her.
Episode 3's whole theme is a massive case of meta Fridge Brilliance. The fight against Satsuki has Ryuko realizing that she must accept how skimpy Senketsu is to use his whole power and what not. The Fridge Brilliance? Its a subtle Take That to the audience! Think about it. Most people will be put off by the show's skimpy and fanservicy designs, as many critics were. Basically, what episode 3 is saying, is that you need to accept that the show has fanservice and let that sink in so you can enjoy the real meat of the story: the characters. By having Ryuko state that Senketsu becomes her skin, it's meant to say that instead of focusing on the fanservice, you focus on the character itself or else the show is not enjoyable, the same way Ryuko can't use Senketsu's full power unless she accepts his skimpiness!
Why did the Rending Scissors, the obvious MacGuffin of the show, fail in the end to even scratch Ragyo's Shinra-Kouketsu? Because the Scissors are a Red Herring both in-universe and out-of-universe. When Nui came for him, Dr. Matoi confronted her with the Scissors and proudly announced them as his life's work to distract her from his real life's work: Ryuko and Senketsu. And we, the viewers, fell into the exact same trap Nui did, assuming the Scissors are way more important than they actually were.
There was an alternate way for Senketsu to stop Maiko after she wears Senketsu to fight against Ryuko. That alternative as revealed in Episode 5 involves consuming the wearer of the Kamui. Considering that Junketsu tries to immediately consume Satsuki when she wore it and Senketsu might have thought about consuming Maiko during the above situation but spared it for Ryuko's sake, Maiko has no idea how lucky she is to be alive even though she gets expelled.
In the past, Nonon was shown to have a pet monkey that sat on her head. Fast forward to her high school days, the monkey is gone and there's a small skull attached to her hat.
And when Jakuzure's uniform is destroyed by Ryuko, everything but the skull and a few bones disappears.
Every time Ryuko uses her finishing move the target's Goku uniform is destroyed. This is a symbol of power, and your uniform determines your caste in society. What this boils down to is Ryuko's finishing move will essentially put the target into poverty.
It's been established that any fight that a Goku Uniform user participates in and loses carries as a consequence the stipulation that the loser is brought down to No-Star, not just the fights that Ryuko is in (e.g. the horde of One-Stars ganging up on the Sumo Club President in episode 8 and then dividing his wrestling gear between themselves when he falls.) Then there's the fact that Ryuko actually rarely instigates fights while at Hounnoji Academy, with most of her battles beginning with a Club President either ambushing her or threatening Mako. And the kicker that most of the student body is happy to stay out of Ryuko's way, but Satsuki either bribes them into fighting her (Two-Star Uniform status to anyone willing to start a club and fight Ryuko in episode 7, with promised Three-Star status if they win) or threatens them (Boxing Club President in the first episode said he would have lost his status anyway if he didn't find Ryuko before the end of the day after she escaped their first fight). Which goes to show just how little of a shit Satsuki gives for anyone who's under her or her inner circle.
With the reveal that Nagita, the News Club President, was really Nui in disguise all along, it makes the moments where he suddenly pops out of nowhere in front of Mako really, really creepy. If she had felt like it, no-one would have been able to stop her from killing Mako.
Episode 16 shows us how far Ragyo can go in her molestation of Satsuki. The question is, when did it start? For how long has Satsuki had to endure that? In Nonon's flashback to their kindergarten days, Satsuki was already a very serious and ambitious girl. What if her speech about building a skyscraper in your mind was about building a wall inside your mind to protect you? What if she had to protect herself from Ragyo's abuse even back then?
Episode 17 seems to further back this up, when Satsuki talks about how she "must've been a kind girl" when she was much younger when Soroi finds out she lied about liking the tea he served her age 5 to protect his feelings. Also compare the little Satsuki who first sees her "wedding dress" to the one who appears in kindergarten, clear difference.
Even more so, Satsuki has had exactly TWO flashbacks in which she acts like a normal, happy, well-adjusted little girl. And in both of them, her Father appears. In all other flashbacks, she acts like the cold, emotionally detached dictator we're all familiar with. This may mean that it was Satsuki's father who was shielding her from Ragyo's sexual abuse. And that after he left/died/WAS POSSIBLY MURDERED BY RAGYO HERSELF FOR THAT VERY REASON.
Ep 18 reveals that Satsuki's personality change was the result of her father telling her the truth about the life fibers and how much of a monster her mother is.
This also puts her speech in episode 3 in a different light. She's already putting up with much worse, so what's a Stripperific outfit to her, especially if it directly benefits her?
When Senketsu was first introduced, he admits that he's amnesiac and doesn't remember much of who he is. Given the true nature of Life Fibers and their view of humanity as food, had he retained his memories, would Senketsu have tried to completely consume Ryuko on their first meeting like the other Kamui?
Considering that all Life Fiber are living, sentient aliens, Senketsu is actually a heroic cannibal. He's been absorbing his kind every time Ryuko destroyed a uniform.
Even more so after he absorbs Nui's severed arms.
In episode 3, Satsuki says she is worthy to wear Junketsu because she is "pure". Come episode 16, and we see the purification ceremony her mother performs on her. It involves her being naked and having her personal space be invaded in the worst way possible. Suffice it to say, Satsuki probably grew up with a warped concept of purity.
Through out the series Satsuki was very serious during her battles with Ryuko. Seeing what was her goal she could not hold back or show mercy. It is very possible that she'd go as far as killing Ryuko if the girl wouldn't be able to defend herself and grow strong fast enough. Here is where the horror settles in, what would be Satsuki's reaction if she would kill Ryuko and then found out that she was really her long lost sister?
Satsuki is so determined to kill Ragyo that she's willing to fight Honnouji students turned on her by Ragyo's Mind Stitching. However, had the Elite Four been Mind Stitched, would she have the same resolve to fight not only her strongest soldiers, but her closest friends?
When Ryuko found out the truth about Senketsu she got really pissed off at the fact that he was born only to kill his own brethren. Ryuko herself had no friends and pretty much no family her entire life. It's something she craves and desires. When she befriended Mako and lived with the Mankanshokus, she was obviously really happy. Now she just found out that she actually has a family. She has a sister and a mother, mother whom almost killed her sister and whom she will probably have to kill to defeat Life Fiber. Ragyo is a horrible person but she is still her mother, her family. Something she craved for her entire life
It's used horrifically and depressingly in episode 20. Ragyo implants fake memories of a normal, happy life with her.
To add to this, the reason for her feeling like this is because her father never told her anything and was in fact, estranged from her. Had he simply been straightforward with her or at least tried to raise her properly instead of putting her in boarding schools, it's possible that Ragyo wouldn't have had that edge on her. In other words Nice Job Breaking It Dad.
You make it sound like he had a choice. Ragyo is incredibly powerful, and could have found him and Ryuko with enough time, effort, and motivation. Best Ryuko be far away when worst comes to worst, like Nui arriving to murder him.
In episode 20, Ragyo puts fake memories in Ryuko's head, of Ryuko living with Ragyo instead of being abandoned. The actual things seen are happy, until you notice one key detail: Satsuki, the older sister, isn't there, at all. It really shows how little Ragyo cares about her daughter.
It might be part of her strategy. If Satsuki were in the fake memories, living together with Ryuko, she could have hesitated in fighting her.
In addition, the fake memories Ragyo implanted had her marrying a lifeless mannequin with a COVERS uniform on it. Now consider the fact that in the first ED, it has a confused Ryuko walking around a lifeless world filled with mannequins shaped to look like real people wearing clothes. The implications of Ragyo's mind rape is staggering.
Then whats with Senketsu hanging near the wedding dress doing there? And the one-stars pretty much everywhere? (look closely in all of the scenes, the walls, the buildings, EVERYTHING.)
The only parental figure that Harime Nui had for all her life was Ragyo. Think about that for a moment.
Nui's character in general is really a mother-lode of Fridge Depressant if you're willing to look back at her scant background details and allow some empathy: She wasn't just infused with Life Fibers as a newborn, she was incubated in an artificial womb of them that made her merge with them as a fetus. Soichiro was nowhere to be seen when she was being gestated and showed no recognition toward her when they fought, so he likely wasn't involved with her life in any fashion, and certainly he had been driven off long before Nui could have developed enough to recognize or remember him later in life, and she grew up completely under Ragyo's sole care, with all the horror that implies. She has no true good relationship with any other character whatsoever, with Rei and Ragyo being aloof taskmasters that only step in to help her when danger to her could result in danger to their cause, and all other characters being either enemies or mindless slaves. She is the only character to actually suffer permanent scarring and loss of limb throughout all the action in the series. She was brought up to believe that she was completely different and separate from humanity, that the Life Fibers and the facilitation of their reproduction cycle is her raison d'etre, and that her only value was in her abilities as a tailor, and when she both loses her arms and finishes the "Ultimate Kamui", her usefulness has culminated in her and her master's eyes, and there is nothing left and nowhere to go for her, and she when muses on how she could be killed in the final battle between humans and Life Fibers, she not only looks ready for the prospect, but relieved by it. She has the worst of both Satsuki and Ryuko's entwined Dark and Troubled Past combined into one whole, turned Up to Eleven, and stripped of all the counterbalancing positive experiences and influences that gave them the initial perspective and strength to challenge their mother. Her entire character arc is reminiscent of Princess Azula's descent into madness from abandonment in her series' finale, except Nui has always been mad since she never even had the illusion of anyone actually loving her, resorting to deliberately driving people, especially those she expresses genuine interest or desire to connect with like Satsuki and Ryuko, to hate her because that's the only kind of care she's ever understood, and there's no one in-universe who would actually feel, let alone show, her any pity.
And in the end, she doesn't even get killed in battle. She kills herself by merging with Ragyo, her mother, the only person who has ever been there for her even if there wasn't any true love shared between them. So twisted....
Ragyo very nearly won in episode 15 without even doing anything. If Ryuko didn't back off then and killed Satsuki, the whole plan to rebel against Ragyo would fall apart. What is even worse is that Ryuko would probably survive being stabbed by Junketsu thanks to the life fibers in her body. Nui would almost certainly realize that Ryuko is a hybrid like herself and then Ragyo would learn it from her. As a final straw, Ryuko would then learn that she murdered her own sister, who was Good All Along, and doomed humanity to subjugation by Life Fibers.
Ryuko might think that Nudist Beach wants her dead. Let's be fair here, Tsumugu attacked her once already and seemed fully willing to kill her to get rid of Senketsu. Then in episode 16 he was also fully willing to go over her dead body to destroy Senketsu. Now that she has learnt that she is a life fiber hybrid, she has even less reason to trust Nudist Beach. Tsumugu was willing to kill her for siding with Senketsu, what would he do after finding out that she herself is life fiber? At least that's what she probably thinks.
It might not have worked the time she used it but... Harime Nui is capable of using Mind Stitching.
In episode 12, Mako expresses surprise that Satsuki knew her name. However, in episode 7, Satsuki had addressed Mako by name several times during her tenure as Fight Club President and fight with Ryuko, and it's also not unreasonable to assume that Satsuki would be spying on Ryuko's life outside of school. (It may have been intended more as an example of being surprised that Satsuki was acknowledging her existence after she fell back to No-Star Rank, however.)
Mako is not the most attentive person in the world, and her mind was elsewhere at the moment, as well.
If Life Fiber-infused humans can heal from getting their heart ripped out of their chest, their head partially cut off and who knows what else, why doesn't Nui Harime grow her eye back?
Possibilities just off the top of my head: Either the eye was completely severed, which meant that she couldn't just reattach it, or her Healing Factor isn't up to snuff (Nui already admitted she isn't compatible with Life Fiber outfits, there could be other deficiencies to her hybrid nature.)
Here's a theory: Life Fiber-infused humans don't actually have an increased Healing Factor. What the Life Fibers allow is more like Pulling Themselves Together on a cellular level (each cell is attached to others with Life Fibers). In order to permanently damage them, you have to both sever the Life Fibers and damage body at the same time. The difference between Ryuko stabbing Nui in Episode 20 and Isshin cutting out her eye, is that Ryuko likely didn't hit anything important, maybe even due to the Fibers moving Nui vital organs out of the blade's path, while with Isshin, he cut out her eye and severed the Fibers simultaneously.
It was established in the same fight that the Scissor Blade completely stops Life Fibers from healing.
Confirmed in Ep 22, as Nui gets both arms cut off, and as she try to reunite them with her body, they "die", allowing Ryuko to absorb the life fibers in them, even Satsuki points this out.
Why doesn't Ragyo ever try to brainwash the Elite Four with her Life Fiber strands? They're powerful, but still normal humans.
Who knows? Maybe she didn't think of it, or they weren't close enough, or it didn't work because they were using their transformed uniforms at the time. Any one of those is possible.
The Elite Four have the most life fiber tolerance, second only to Kamui users. Most probably, it would take quite a lot of effort to ensnare them, especially since they are a lot less volatile and collected than Ryuko.