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.
I'm not sure exactly which tau novels are on your list, but 'Tau: Fire Warrior' is also quite popular. It offers a detailed look at the tau society, their military strategies, and the challenges they face. The story is engaging and full of action scenes that keep the reader hooked.
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.
Visiting a local library or a well - stocked bookstore is also a good idea. The librarians or the bookstore staff can often guide you to more resources about tau novels. They might even be able to recommend similar novels if you like the tau ones. Plus, you can physically browse through the books and get a feel for them.
There's no one - size - fits - all answer. Some tau novels might be great for young readers who are into science - fiction and alien cultures. They can learn about a different kind of society, its values, and how it functions. However, if a tau novel has a lot of complex concepts, or if it has some scenes that could be considered a bit intense (like battle scenes or political unrest), it may be better for older young readers, say those in their early teens or older.
I'm not entirely sure specifically about the origin story of MTF Tau 5. It could be something unique within a particular fictional universe or organization that I'm not familiar with. Maybe it's from a game, a book or some other form of media.
One of the best tau novels is 'Fire Caste' by Peter Fehervari. It delves deep into the tau society, exploring the different castes and their functions within the tau empire.