Mizu and Akemi's relationships with sex and sexuality actually makes my stomach hurt. Spoilers below the cut
Mizu sees sex as weak, seeing Madame Kaji's house as a place of discomfort and shame. Mizu seeing the men in there being submissive, and her immediate reaction being *disgust.* When she looks in one of the peepholes to see a man laying with both a man and woman, her eyes widen and she shuts the peephole like she's worried that if she looks too long she might not ever leave.
The one time we see Mizu having sex (I assume it's the only time she had sex at all), she isn't rough, she isn't in control, she's allowing herself to be soft with her husband. She kisses him and she lets him touch her, and this is the most vulnerability we ever see from her. The fact that she is on the bottom, that she is the receiving partner, that she *initiated at all* tells us so much about who she is when she allows herself to be happy. When she lets herself relax enough to be happy, she is soft. Not delicate or refined, but soft and gentle and loving. This is who she is when she lets herself relax.
However. When she shows her husband her skills with a blade and beats him, she kisses him while holding his own blade to his throat. This is who she is when she is relaxed, and *unguarded*. Loving and skilled, and a little kinky, she is embracing this version of herself that she refused to acknowledge for years. And then her husband pushes her off and calls her a monster, and for the first time the insult is directed at *who* she is rather than *what* she is. When Mikio refuses to help her fight the people trying to kill her, the person who let herself love and be loved, who let herself relax and let down her guard, who let herself be truly and deeply vulnerable dies. Her walls come back up and ever since she has refused to let any kind of love distract her (let alone sex).
And so she sees the men at Madame Kaji's house being open and vulnerable, she reacts with disgust. She is disgusted by the vulnerability she once showed, and by the weakness these men put so proudly on display. She doesn't react in disgust to the man laying with both genders, instead she reacts with an immediate shutdown because she knows that if she thinks about it too long she will realize that she still has desires. She cannot allow herself to become more than the empty shell that she carved herself into. She cannot let herself want anything other than revenge, and she cannot let herself be vulnerable again.
Akemi is the opposite. Akemi is so used to the feeling of vulnerability that she uses it as a disguise. The vulnerable young princess who's naive to the world, so she needs a husband who knows the world better. The vulnerable girl who cant pick a place to work as a prostitute, so she needs someone to negotiation her contract/take her different places. The vulnerable girl whose contractor will beat her if she doesn't service Mizu.
Akemi doesn't have the mental guards up that Mizu does. Every emotion shows plainly on her face, every emotional wound cuts straight to her core. Even when She bites her tongue in restraint She might as well be screaming. She cannot afford mental guards, she can't afford to appear as anything other than fragile, or she loses the one advantage she has.
Akemi uses her body as a bargaining chip, showing such a vulnerable part of herself first to Taigen, who misunderstands her point completely and ditched her for a half baked revenge quest. (Taigen they could never make me like you.) The second time she's intimate with someone, it's clear she finds the person repulsive, and that she's physically intimidated by him. She's quick enough with her wit to find a way out of the situation without revealing herself, even using previous compliments as instructions for how to entice him.
Throughout the story Akemi is told time and time again that she only has two options: to be the wife of the Shogun's son (who has been rumoured to be ruthless in all forms, including in a marriage) or to become a prostitute and sell her body. Everyone tells her that her choices don't matter, and that she should go with the lesser of two evils. Even Mizu would rather become a man than live as a woman in her quest for revenge. Everyone tells her she has no choice, except for Madame Kaji. Madame Kaji presents a way for her to be the governor of her own life, she shows Akemi that she doesn't have to just *live* as a wife, she can thrive. All Akemi needed was to be told that her choices matter, and that she can decide what she wants to do without remaining helpless.
With that lesson, Akemi meets with her new husband, and upon learning about his speech impediment, she immediately shows sympathy to gain his trust. She goes to bed with him in a display of false intimacy, she isn't showing her true colors to him, she's gaining favor in order to gain power.
At the same time as Akemi going to bed with her husband, Mizu reforges the steel from her sword. She stands nude in front of the fire to display the parts of her that she is ashamed of (literally and metaphorically). She is coming to terms with who she is. Mizu reforges her steel and herself while Akemi buries herself. Akemi buries her real emotions, once again using her body as a bargaining chip.
I just find the parallels interesting. While Mizu's nudity is used to represent genuine vulnerability, Akemi's is used to represent a facade.