It could be an old enemy who has come back with new and more terrifying powers. For instance, Orochimaru might return with some kind of jutsu that can directly target Naruto's mind and create unfathomable fears in him.
In some cases, it could be Naruto's own inner demons. He has been through so much in his life, and all the traumas and pressures he has faced could manifest as fear within him. Maybe in the fanfic, his past experiences resurface and become the source of his fear.
Chapter 192, ", Heavenly Gene", is the clearest early answer because it turns Lacroix's situation into a concrete plot event. A useful checkpoint is the way the scene starts with He once again lamented in his heart, he really shouldn't have let... and follows through with A person who looked like a researcher approached him: "Chairman Ge....
Chapter 329, ", Heijian Star Joins the Alliance", is the clearest early answer because a shaky connection becomes usable in the plot. Early on, Galaraldo really left a big surprise for both Tianma Star Sector and.... By the end, Voyagers', up to now, were not something the Alliance could mass....
Chapter 342, ", 4 years", is the clearest early answer because it turns Army Group's situation into a concrete plot event. The chapter turns that into something concrete by moving from Four years had flown by, and this marked the fifth year that Lucy Lee... to Fifty million Star Realm Armed Forces, or a billion native troops –....
Chapter 182, ", The Technical Expert You Wanted", is the clearest early answer because it turns Rage Owl Star's situation into a concrete plot event. A useful checkpoint is the way the scene starts with After he was hired, his life began to feel comfortable. and follows through with Then, he and his family endured a hellish escape, heading north until....
Chapter 297, ", The Rotten Dragon", is the clearest early answer because it turns Psychic Cultivator's situation into a concrete plot event. Early on, He had heard that the Gu Family was already discussing selling their.... By the end, Evacuate in an orderly fashion!" This voice seemed to carry a certain....
Chapter 270, "The Demon Hunter of Blackbird City", is the clearest early answer because it pushes Western Desert into a new phase or setting. Early on, Ilan Bird looked up at the dark building in the rain ahead and, after.... By the end, Have a cup of hot water, and then we can talk in detail." ....
Chapter 135, ", On the Verge of Collapse", is the clearest early answer because it turns Rubbish Town's situation into a concrete plot event. A useful checkpoint is the way the scene starts with Understood," Perbov said, "I will lend you a hand. and follows through with The departure wasn't yet widespread or on a large scale, but it was....
Chapter 256, ", you've guessed it, right?", is the clearest early answer because it turns Nes Luman's situation into a concrete plot event. The setup is When Gu Hang received the battle report a step ahead, he knew that..., but the pressure keeps building through He said to his mother, who appeared somewhat haggard and disheveled,....
Chapter 205, "The Soldier King Can Achieve It", is the clearest early answer because it turns Demon Engine's situation into a concrete plot event. A useful checkpoint is the way the scene starts with It must be emphasized that he was not at his full strength,... and follows through with But Soldier King, that's exactly what he could do..
Chapter 272, ", this is reasonable", is the clearest early answer because it turns Winter's situation into a concrete plot event. The chapter turns that into something concrete by moving from A bird leapt out of the curtain of rain and flew high into the... to All Winter had was a short-barreled laser pistol with almost depleted.... What makes it stick is that the chapter closes with When Winter and Bird were discussing the operation plan, they didn't whimsically decide to involve a child.