Since I'm not familiar with a specific 'Niwa massacre', it's possible that this is a very specific event within a particular region or community. It could be related to a family feud that escalated, or it might be part of a larger historical context such as colonial - era violence or ethnic tensions. If there are local historical archives, newspapers from the time period, or eyewitness accounts, those would be the best sources to uncover the real story.
There probably are. Fanfictions about female Daisuke Niwa could range from light - hearted comedies to more serious dramas. She might be the hero in some stories, saving the day with her intelligence or courage. In other fictions, she could be the one in need of rescue, which would then lead to a story of her learning and becoming stronger.
Archive of Our Own (AO3) is also a great place. It has a large collection of fan - created works. There, you can filter the search results to find the most relevant female Daisuke Niwa fanfictions. You might need to dig a bit, but it's worth it.
Again, without knowing precisely which 'Niwa massacre' is being talked about, it's hard to say for sure. But if it was a significant event, there should be some form of historical records. These could be in local archives, old newspapers, or personal diaries of people who were alive at the time.
As of now, the Genshin manga is not finished. The story is still evolving and there's more to come for fans to enjoy. The creators are taking their time to develop a rich and engaging narrative.
There's no definite answer yet. It might continue if there's enough demand and the creative team has more story to tell. But it could also stop if they feel they've completed the story arc.