I'm not entirely sure as I haven't specifically played it. But generally, a visual novel often has a story with characters and different plotlines. It might involve themes related to the title, perhaps about female characters ('onna kanbu') in some sort of context, which could be related to a dark or 'aku no' (evil or bad) situation. However, without more information, it's hard to be more precise.
Since I don't have direct experience with it, it's difficult to say for sure. However, some visual novels have unique art styles that set them apart. Maybe 'aku no onna kanbu visual novel' has a distinct art style that enhances the mood of the 'aku no' (dark) theme and the portrayal of the female characters ('onna kanbu').
I'm not sure who Aku specifically is. Aku could be a person with a great imagination who tells all kinds of stories, like adventure stories, fairy tales or even true - life stories.
It could be someone from the Naruto universe who doesn't like Naruto's newfound fascination with Aku. For example, Danzo might see Naruto's interest in Aku as a threat to the stability of the village and try to stop Naruto from further exploring Aku - related things. So, Danzo could be the main antagonist in this case.
The character of Aku could be developed in a 'pregnant Aku in Samurai Jack fanfiction' by exploring how he interacts with the world around him differently. He may become more reclusive as he doesn't want others to see his 'weak' state. Or he could become more aggressive in trying to protect his pregnancy, which would be a new aspect of his character. Also, his relationship with his own power might change. Maybe he has to find new ways to use his magic that don't harm the unborn, which would force him to grow and adapt in ways he hasn't before.
One idea could be a crossover where Aku accidentally opens a portal to the Naruto universe. Naruto, being the curious and brave ninja he is, decides to explore Aku's world. They could start off as enemies, but gradually come to understand each other's motives and end up teaming up against a greater evil that threatens both of their worlds.
In Japanese novels about shogun and ona, one characteristic is the detailed portrayal of the social hierarchy. The shogun represents the highest power, and the position of ona (women) varies greatly depending on their family background and social status. For example, in 'The Tale of Genji', the female characters' lives are closely tied to the power structure. Another characteristic is the emphasis on cultural traditions. Many such novels depict traditional Japanese arts, like tea ceremonies and flower arranging, which are an important part of the shogun - era culture.
I'm not sure specifically as I haven't read it in detail. But generally, it might be about the relationship between a negative hero and the demon army's officers.