Maybe there's a curse placed on Naruto that is causing him to die secretly. It could be related to some old, forgotten shinobi magic. In the fanfiction, the curse could be slowly draining his chakra and his very essence. He'd be struggling to keep up his normal appearance while he desperately tries to find a way to break the curse.
One possibility could be that Naruto has been poisoned by a new and unknown enemy. This poison is slowly eating away at his life force, and he's trying to hide it from his friends and family so as not to worry them. He might be secretly seeking a cure while still fulfilling his duties as Hokage.
In this fanfiction, it could be that Naruto's overuse of the Nine - Tails' power has led to some unforeseen consequences. The chakra of the Nine - Tails might be slowly corrupting his body from the inside out. He's keeping it a secret because he doesn't want to lose the trust of the village that has come to rely on his power. He's secretly looking for a way to reverse the damage while still being the strong leader everyone expects him to be.
If you want the clearest chapter reference, go to Chapter 211. Early on, Advanced Repair was even more outrageous, costing a whole 30 points.; later, the chapter leans on Not to mention the 50 points for Supreme Repair..
Chapter 172 is the strongest chapter-level answer because it starts from Not only Shu Yan, but the entire internet was shocked when they saw Su... and follows through on Where's the chaotic scene I was anticipating?. The payoff is that the chapter closes with "Jiaojiao, are you surprised?
If you want the clearest chapter reference, go to Chapter 168. Early on, Su Yinwan spoke those words with a pitiable expression, then lowered her...; later, the chapter leans on The next second, a crisp notification sound rang in her Divine Sense,....
Chapter 190 is the strongest chapter-level answer because it starts from Several people who didn't understand fell silent. and follows through on Because he saw the pack of cigarettes pinched between Jiang Li's fingers..
Look to Chapter 215 for the clearest answer. It begins with Jiang Li let out a light sigh and tried to adjust her posture., keeps building through I'm not dismissing you, I just think there's no need for you to cry." Wen..., and lands on He originally just wanted to see if there was a chance to.
The best chapter pointer here is Chapter 168, "Gu Family in the Capital". It opens with Su Yinwan spoke those words with a pitiable expression, then lowered her... and closes on The Gu Family had strict family education; even if Gu Yu was the only heir....
A practical answer is Chapter 158, because it turns the idea into a concrete scene. The chapter opens with Reluctantly, Jiang Yan had no choice but to forcibly join the group for..., adds pressure through Don't make me laugh, Jiang Li looks better even without makeup than she..., and ends on we're.
The best chapter pointer here is Chapter 156, "Group Morning Run!". It opens with Flash Change, who was always tardy, was late again today. and closes on Soon after, the meditative He Yun also walked over..
If you want the clearest chapter reference, go to Chapter 179. Early on, Everyone originally had no expectations for the gifts that Su Yinwan...; later, the chapter leans on Although they felt there might be a catch, a few people still curiously....
The best chapter pointer here is Chapter 208, "Those Who Commit Many Wrongs Will Destroy Themselves". It opens with Jiang Yan clicked his tongue, "What's this about money? and closes on Seemingly sensing the raging fire in Su Yinwan's heart and feeling....