One idea could be that Kurama is trapped in a special jail within Naruto's mind. Maybe it's a result of some dark magic or a side effect of a new jutsu Naruto attempts. In the fanfiction, Naruto could be desperately trying to find a way to free Kurama while also dealing with the internal chaos that Kurama's imprisonment causes within him.
In a fanfiction scenario where Kurama is in Naruto's jail, it could be a situation where Naruto has unknowingly created this jail due to his own insecurities. He fears Kurama's power getting out of control again, so his subconscious mind forms a jail. Kurama, on the other hand, could be trying to communicate with Naruto to make him understand that this is a wrong approach and that they need to work together as they did before.
A possible fanfiction plot could involve an enemy who manages to trap Kurama in a jail inside Naruto. This enemy might be trying to use Kurama's power for their own evil purposes. Naruto, realizing what has happened, has to embark on a journey within his own mind. He has to face his fears and insecurities represented by the jail and find a way to break Kurama free and defeat the enemy who set this all up.
Chapter 300, "You're retaking the college entrance exam?!", is the clearest early answer because it turns Jiang Zhao Yuan's situation into a concrete plot event. The chapter turns that into something concrete by moving from I dropped out." Jiang Li said calmly.
Chapter 181, "Are All the Weibo Followers Police?", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. It opens with Xiang Hao rushed to the police station as soon as he saw the trending...
Chapter 275, "Five Defects and Three Shortcomings", is the clearest early answer because it turns Officer Xu's situation into a concrete plot event. The chapter gives readers a real answer by opening on Hu Zi was exceptionally cooperative, and within half an hour, all the...
Chapter 350, "Methods to Improve the Peak of Cold Resistance, Moao's 10th Town, Beishuo Yang Fa, Nightmare, Lu Yun of East Ridge", is the clearest early answer because it turns Xia Hong's situation into a concrete plot event. It opens with Hmph, the Nine Towns have had an agreement long ago: if a Xianyang... and closes on Evidently, the other party didn't believe his self-introduction just....
Chapter 430, "I Quit", is the clearest early answer because it turns Sister Li's situation into a concrete plot event. The chapter gives readers a real answer by opening on Hey, do we join a team that's short on members, or do we form our...
Chapter 333, "Silver Mine from the Heavens, Yu Yao and Yu Sheng, No Need for an Ox Knife to Kill a Chicken [10,000-Word Mega Chapter Continued]", is the clearest early answer because the violence around Xia Hong becomes final instead of hypothetical. It opens with This valley is located inside the mountain of Twin Dragon Mountain,... and closes on Chen Ying saw his face full of excitement and, recalling how Xia Hong....
Chapter 272, "Jiang Fugui", is the clearest early answer because it turns Jiang Cheng's situation into a concrete plot event. Early on, Lin Manru held the phone for a few seconds, expecting her daughter.... By the end, So, they made him a temporary ID card, temporarily changing his name....
Chapter 310, "Sister, Eat More", is the clearest early answer because it turns Jiang Yan's situation into a concrete plot event. Early on, Jiang Yan snorted, "Then, Grandpa, you just talk less, so Uncle Three.... By the end, Later, when her second uncle became successful, the old master saw....
Chapter 349, "Attempting to Cheat, East Ridge's Strength, Lu Yang's Tactics", is the clearest early answer because it turns East Ridge's situation into a concrete plot event. It opens with The five people, including Zhu Tong, were all bowing their heads at... and closes on Bringing only Zhao Hu and three others over, how could he rest.... The key payoff is that the chapter closes with Seeing the five leaders' eyes all gathered on him, a faint gleam flashed in the depths of Lu Yang's eyes.
Chapter 126, "The Production Team Actually Played Dirty on This?!", is the clearest early answer because it turns Director Sun's situation into a concrete plot event. The chapter turns that into something concrete by moving from Wen Jiaojiao initially wanted to cause trouble.