A common plot is that they are sent back in time by some sort of magic or a powerful jutsu gone wrong. Once in the past, they have to find a way to get back. Along the way, they end up changing little things that have a big impact on the future. For example, Naruto might accidentally teach a young ninja a new move that wasn't supposed to exist yet, and Hinata could inspire a young girl to be more assertive, which then changes the social dynamics in the future.
One popular plotline is that Naruto and Hinata travel back to the time when the Uchiha clan was still intact. They try to prevent the massacre from happening, which changes the whole future of the ninja world. Another plotline could be them going back to their childhood days. Hinata gets a chance to be more confident around Naruto earlier, and Naruto realizes Hinata's feelings sooner, leading to a different relationship development.
In some fanfictions, they time travel to the era of the First Hokage. There, they learn ancient ninja techniques and use that knowledge to better their own time. Naruto might also use this opportunity to understand more about the origin of chakra and how it was used in the past, while Hinata could gain more confidence by seeing strong female ninjas in that era.
Chapter 324, "Early Drills, Surge in Cold Resistance Level Members", is the clearest early answer because Cold Resistance Level finally turns buildup into a real advancement. The chapter gives readers a real answer by opening on After Xia Chuan's two-month-long transformation, the outer city has... and ending on If you want to die, go ahead, but I'm not joining in your madness."....
Chapter 288, "On the March, Hou Hu's Wrath", is the clearest early answer because it turns Xia Chuan's situation into a concrete plot event. The chapter gives readers a real answer by opening on A bit faster, it's been half an hour and we've only covered a... and ending on He froze momentarily, looking up at Xia Chuan with a puzzled....
Chapter 335, "Songyang Ridge, Seven Houses Surrender, First Batch of Silver Arrives", is the clearest early answer because it pushes Songyang Ridge into a new phase or setting. The chapter gives readers a real answer by opening on Everyone, move to the sides and make way for the army to pass. and ending on Especially following, Xu Ning and Li Longkai's question and answer....
Chapter 276, "Integration of Soldiers and Hunters, Military System, and Roll Call Hunt (Part 3)", is the clearest early answer because it turns Peng Bo's situation into a concrete plot event. It opens with Chen Yingyuan and Peng Bo arrived late, clearly not hopeful, out of... and closes on Once the structure of the Cloud Jiao Army is complete, set off to....
Chapter 134, "Being able to accompany Miss Jiang is my good fortune", is the clearest early answer because it turns Jiang Yan's situation into a concrete plot event. The chapter gives readers a real answer by opening on After a brief noon rest, the production team was up to their antics...
Chapter 45, "Give a Sweet Date and Then a Slap", is the clearest early answer because it turns Shu Yan's situation into a concrete plot event. The chapter gives readers a real answer by opening on Helplessly, Jiang Yan had no choice but to step on the accelerator.
Chapter 288, "On the March, Hou Hu's Wrath", is the clearest early answer because it turns Liu Yuan's situation into a concrete plot event. The chapter gives readers a real answer by opening on Alright, urge the army to speed up, I'll keep an eye on things from... and ending on Visually, the so-called transport team appeared much more impressive.... In story terms, the chapter closes with Most of Longyou is flat plains, and there are few places to hide troops and ambush.
Chapter 158, "It's Time to Recruit Someone Who Understands Mysticism to Work Here", is the clearest early answer because it turns Flash Change's situation into a concrete plot event.
Chapter 326, "Divide and Annihilate, Shattering Divine Light—The Trump Card Arrives! (3)", is the clearest early answer because it pushes Shattering Divine Light into a new phase or setting. The setup is Despite being restored to its normal size, the surface of the Striped..., but the pressure keeps building through Many Cold Beasts around it turned their heads to look, and upon....
Chapter 181, "Are All the Weibo Followers Police?", is the clearest early answer because it turns Wanwan's situation into a concrete plot event. The chapter turns that into something concrete by moving from Xiang Hao rushed to the police station as soon as he saw the trending...