The protagonist of this novel would be me. Before the time-travel, I was terrible at history — I understood neither the grand currents nor the succession of dynasties. After traveling back, I'd find myself living along the banks of the Han River in the rugged mountains of the Qinba range, "unaware of the Han dynasty, let alone the Wei or Jin." Before the time-travel, I was terrible at geography too — couldn't make sense of China's terrain. I'd end up in a small village deep in the Bashan Mountains, where the locals know nothing of the world beyond the next two ridges.
Given how dire the situation is, the time-traveled me would have no choice but to muddle through life. To live, I'd need a setting; for a setting, I'd need a broader backdrop — historical and geographical, as we discussed in the first paragraph. But what kind of backdrop? To put it crudely, first I need a central theme. The protagonist needs a purpose for going back, even though novels always make it seem like the protagonist discovers it gradually (or quickly) through life after the crossing. But the truth is plain: the central theme arrives even before the protagonist's name — and speaking of which, I, the protagonist, don't even have a name yet.
My first thought was to travel back to the late Ming and early Qing, wipe out the Jurchens, and prevent the Qing dynasty altogether — inspired by reading Stealing the Ming. But I don't know that period of history — in fact, I don't know any period. I have no knowledge of military history, technological history, or the history of daily life. Honestly, I can't even figure out how the protagonist would go to the bathroom after going back. Better drop it. Another popular theme is traveling to the Xining era of the Northern Song to meddle with Wang Anshi's reforms. The central idea of such novels is to develop capitalism in China. I despise capitalism, so I couldn't possibly write that. In short — can't write them, don't want to write them. Not a single popular time-travel theme works for me.
So what central theme should there be? Would it work to have none at all? That's one option. I could send the protagonist back, and year after year, through the cold and the heat, he'd just farm and meditate in the mountains. He'd accomplish nothing and have no idea what to accomplish. He can't even figure out the geography or the history. I'd give him parents, arrange a marriage, throw in a few companions — none of whom advance the plot in any way. And when it's written, it's done.
That would make it less of a time-travel novel and more like pure literature — even a touch existentialist. But then, I rather look down on pure literature. So what then? This is life. You write a time-travel novel that has absolutely no impact on human existence or the vast cosmos. Here, the plot doesn't develop; time flows silently. Sometimes great waves surge from the depths of the heart, swelling with the desire to do something for the world — then subsiding again. In the end, the protagonist dies, or simply grows old. That, perhaps, is what I want to write.