Aspects of Aizen - Yin (female aspect):
Aizen has surprisingly many instances in which he stabs, slashes, or orders the killing of a female character.
Scenes involving his violence toward female characters feel a little different than his violence toward male characters - less like a fight, and more like an act of resentment.
Let's look at examples:
Rukia - he orchestrates her execution so he wouldn't have to kill her himself, yet this plan fails, and he has to extract the Hogyoku from her literally with his own hands. But it is not the way he ruins her self-confidence (starting years earlier with the tragedy he brought upon Kaien and his wife), not even about how he pierces Rukia through the chest to get his hands on the Hogyoku. The most striking scene is when he carelessly and disrespectfully grabs her by the collar, like Rukia had no will on her own. He drags her around, as though she were his property. He keeps conversing with Ichigo, not with Rukia while treating her like an object. And when the Hogyoku is extracted, he orders Gin to kill her. He still refuses to make an effort to kill her himself. That's how little he cares about Rukia's life.
Momo - here the scene borders on intimate as Aizen deliberately cultivated the fake trust between them. He lures Momo close, stabs her while thanking her, keeping his facade of kind Captain Aizen till the very end. However, his initial plan was for Hitsugaya to kill her. He, again, didn't want to kill Momo himself. He didn't find her worthy of his sword. Of his truth. But when he does finally stab her, he claims this is mercy. He doesn't believe that Momo would be able to go on without him. Also, again (like with Rukia) he speaks of chopping Momo's body into pieces in front of someone who cares about Momo - in front of her friend Hitsugaya. So he not only discards Momo as a pawn he used, he additionally uses her as a trigger for another character.
And then comes the second time he tries to repeat the same model. During Fake Karakura Town fight, Aizen orchestrates everything the way that Hitsugaya stabs Hinamori (as Aizen initially wanted him to). So this says two things: Aizen still doesn't see Hinamori as a person who might have grown stronger after the suffering he caused her, he sees Hitsugaya that way - that is why he mentally tortures him. And he still uses Hinamori much like a mindless puppet. Even worse in this case, because here Hinamori isn't just brainwashed by him, she is basically injured and unconscious so he probably has to physically place her in his place for Hitsugaya to stab her. That is very similar to dragging Rukia around like a ragdoll. Also, it solidifies how Aizen has absolutely no sentiment for his ex-subordinate (unlike Gin or Kaname).
Hiyori - during Pendulum Arc Hiyori is getting Hollowfied alongside Kensei, Shinji, and the others. Hollowfication itself, in her case, is an unfortunate coincidence (Urahara ordered her to go there) but what happens during Aizen's conversation with Shinji is, again, the same pattern we have already seen. Aizen knows Hiyori is Shinji's friend. So to trigger Shinji, or perhaps to emotionally hurt him, Aizen orders Kaname to attack Hiyori. He doesn't do it himself. Of course not. That would be below Aizen. And he doesn't do it because Hiyori poses any danger, he does that after she speaks Shinji's name. While Hiyori is cut down, Aizen pays her no attention. He casually speaks to Shinji. And his provocation works.
Later, in Fake Karakura Town Arc this provocation is repeated by Aizen. Hiyori is targeted by Gin, however, Aizen comments on Shinji's reaction to her getting bisected. So it is not about Hiyori. Her bond with Shinji is used to get to Shinji before his fight against Aizen even starts. But Shinji manages to collect himself emotionally, probably knowing what Aizen intended.
Harribel - the only female Espada at the time of Arrancar Saga, and also the only Espada Aizen strikes down with his own sword. Not because she disobeyed him or betrayed him. No. Because she disappointed him. Bored him. Couldn't finish her fight fast enough. The fact that Aizen cuts her down himself might look like respect. He likes to tell his opponent that even drawing his sword against them IS a form of respect. However, the way he goes about it is totally disrespectful. Using hypnosis on her to stab her in the back. Telling her: "Don't make me swing my sword twice at someone like you." There is no respect in his words, and the treatment she got for her loyalty. The disrespect in this case might originate from multiple factors, not purely for her being a female warrior. Aizen is generally disappointed with Arrancars as lesser beings than himself, coming from Hollows. Aizen also doesn't accept reliance, and Harribel, sharing trust and respect with her three FracciĂłn, represents trust, teamwork, support - things Aizen does not appreciate.
Orihime - she seems like an exception at first, as Aizen expresses interest in her power, almost appreciating what she is capable of. However, this quickly got dismissed by Aizen himself. He is not using Orihime's powers for any of his plans, and he treats her as a bait to lure Ichigo into Las Noches so he can further pushes his progress. So the moment Aizen realizes a female could be exceptionally powerful, he keeps her at a distance. Locks her up in her room. Allows potential harm to be directed her way (Loly and Menoly), and leaves her in a position of damsel to be saved. Telling her than a girl like her only needs to smile, which reads like an attempt to diminish her contribution to the war.
I am not counting in Lisa, Mashiro, and Soi-fon into this because in these cases the fight doesn't seem to vary from Aizen's encounter with male characters.
Yoruichi is an honorable mention, not because she gets attacked by him in any particularly cruel or personal way, but because during their 3 vs 1 battle it is Yoruichi who gets the most ignored verbally by Aizen. He has a dialogue exchange with Urahara, he comments on Ishin's Getsuga, but Yoruichi's comment about her legs (which is jokingly flirtatious on purpose to defuse Aizen's god-level ego at that moment) is met with a wall of Aizen's emotionless, flat reaction. Also, during the same encounter, Urahara is the one who gets the most of Aizen's attention, while Yoruichi is being clearly ignored conversation-wise. I think this is telling. It shows whom Aizen would rather treat as a conversation partner.
From these examples we see that female characters often work as extensions or emotional access/weaknesses of male characters he interacts with. He recognizes the connection, and uses it. He rarely engages in a longer conversation with a female character. He doesn't seem to see them as worthy or likely to progress after challenging them, he rather discards them when not useful anymore.
At the same time, there is no significant female character in Aizen's circle of closest subordinates. He is often accompanied by Gin and Tosen after they leave Soul Society. The Espada has only one female member. And his Arrancar maids - Loly and Menoly - get no attention from him, and are treated rather coldly, and strictly.
Interesting fact is that his two closest followers - Gin and Tosen, both have strong bonds with female characters. Kaname's whole philosophy of justice is inspired by his friend - KakyĹ, and his need for revenge is a reaction to her getting brutally murdered.
Similarly, Gin's motivation began with Rangiku getting hurt by Aizen's lackeys. He is following Aizen for revenge, just like Kaname, and this revenge would be irrelevant if the bond with a female character had never existed. Aizen gets a glimpse into a power of that bond when Rangiku's cries over Gin's mutilated body. And what is Aizen's response to that scene? He tightens his grip on his sword, ready to strike her down. Just like he did to Gin.
As we see, Aizen not only targets multiple female characters, he also tends to target male characters who has a strong, personal connection to females. His main opponent are:
Ichigo - who inherited his protectiveness from his deep bond with his mother, and who also shares respectful and loving bonds with both Rukia and Orihime (both targeted by Aizen).
Urahara - who has a strong partnership with Yoruichi, and who also tried his best to befriend Hiyori during the pendulum arc.
These two characters, thanks to their connections (including, but not limited to, women) defeat Aizen in the Arrancar Saga.
Other characters, to whom Aizen seems to be particularly cruel toward are Hitsugaya, and Shinji. And again, both of them share strong, mutual bonds with female friends (Momo, and Hiyori). I already covered Kaname and Gin, I just want to add that in both cases Aizen kill them personally, as if punishing them for choosing the connection over his goal.
All the instances mentioned above, can suggest some sort of resentment or jealousy that Aizen carries toward other male characters who share emotional closeness with female characters. Or who perhaps are simply able to create meaningful, deep bonds with an aspect opposite to their own.
This resentment could be interpreted in a philosophical way, rather than as a simple misogyny. What he attacks is what the female characters symbolize.
Femininity in Bleach is connected with connection, care, attachment, protection of others and sacrificing oneself for the others (Masaki is an example, and how she defeats White by letting him bite her). Emotional intelligence represented by Orihime is another meaningful theme connected to femininity. With this comes compassion, empathy, supporting others and letting others rely on you emotionally (again, Orihime shows this, but also Ikumi, and Kukaku). And we already briefly touched on sisterhood, teamwork, motherhood and camaraderie represented by characters who are able to bring others together (Harribel, Matsumoto when supporting Orihime, Rukia training with Orihime). This places femininity as an important factor in creating community, and bonding people together, not by force, but by support and understanding.
Naturally, Aizen despises and lacks all these aspects, and they might be threatening to his belief in extreme individualism and self-sufficiency, his hate of dependency and reliance, refusal of being understood and connecting with others. What female characters represent in Bleach conflicts directly with Aizen's self-construct.
This could hint at Aizen's lack of internal balance between female and male aspects of self (anima and animus in Jungian interpretation, or yin and yang in thaois).
Yang - in taoism is a male aspect, the light (Aizen is compared to being like the Sun), white color (Aizen's color for the most of the Arrancar Saga), expansion, active energy, progress, strength. These are all aspects that Aizen clearly shows through the series.
Yin - the female aspect associated with the black (Shinigami color), the night, the moon, the stillness, passiveness, acceptance, introversion, the energy directed inward, intuition, treachery. Aizen exhibits only some of these aspects.
However, his power and his sword strongly resonate with Yin aspect (illusions, moon, secrecy), which makes me believe that Kyoka Suigetsu embodies Aizen's anima (female aspect), which he never fully accepted, internalized, or embraced. This creates an interesting contradiction: the power that defines him originates from aspects of himself that he appears unwilling to consciously acknowledge. Perhaps this is why we never see his Bankai.
Psychologically, this lack of acceptance of his own Yin/female aspect is self-destructive and keeps him from connecting.
The imbalance within Aizen may be caused by the absence of a maternal figure in his formative days, however this is speculative.
Whatever the reason, Aizen in multiple instances exhibits a dismissive attitude or violent rejection toward characters who are connected with female characters naturally, or toward female representation themselves, suggesting that he externalizes the rejection of a part of his own nature. But he also seems to envy what he dismisses because it makes him incomplete. Hollow. As three hollow holes he carries within himself after his final transformation.
Aizen's internal conflict is becoming the most visible right after his defeat, when his power is starting to fade instead of evolving again. This clearly shows his lack of self-understanding. And if we interprt Kyoka Suigetsu as the manifestation of his anima then his sword crumbling down gets the new meaning.
