There could be. Check out various fanfiction communities. They often have filters or tags that can help you find the more family - appropriate stories about Eren and Historia in this situation. It may take some searching, but they do exist.
It might also be a character who has a more complex or unexpected connection to Historia. For instance, there could be a plot twist where a character who was thought to be an enemy turns out to be the father, adding a whole new layer of drama to the story.
Perhaps the fanfiction could focus on the reactions of the other characters. For example, Eren might have complex feelings about Historia's pregnancy, as it could symbolize a new hope for humanity in a way, or he could be worried about her safety in such a vulnerable state.
One idea could be the two of them preparing for the baby. Historia might be learning about different parenting styles, and Eren could be building a nursery. It could show their growth as individuals and as a couple.
It's fairly common. Fans often look for more content related to their favorite shows. Since 'Attack on Titan' has a large and passionate fan base, there are a lot of fanfics available. 'Aot' fans might watch (read) these fanfics to explore different scenarios that the official story didn't cover. For example, they might want to see how a certain character would react in a different situation or what would happen if a major plot event had a different outcome.
A 'historia visual novel' could be about various things. It might be a story set in a historical context, with characters and plots that unfold in a way typical of visual novels. It could focus on a particular era, like the Renaissance or the Victorian age, and tell a fictional story with elements of that time's culture, society, and events.
There could be various fanfictions. Maybe some that focus on alternative endings, like ones where certain characters survive who didn't in the original. For example, a fanfiction where Erwin survives and leads the Scouts in a different way.
Yes, there are quite a few. You can start by looking on fanfiction.net or Archive of Our Own. Some fanfictions might explore their relationship in an AU (alternate universe) setting, like a modern-day scenario where they meet and get married, while others could be more in line with the original story's themes and settings but with a different plot twist leading to their marriage.
There could be some, but it really depends on the market and the fan base. Since visual novels are a diverse genre, those with a historical focus might not always get the same level of mainstream attention. But in the communities dedicated to visual novels and historical fiction, there may be some well - known 'historia visual novel' titles that are highly regarded for their storytelling, art, and historical accuracy.