Well, in the fanfiction, since Naruto is sick, Yamato might recall all the times Naruto has been strong and determined. He could be determined to see that strength return. Yamato might seek out special herbs or medical ninjutsu knowledge to cure Naruto. And during Naruto's sickness, they could have deep conversations about Naruto's dreams and fears, strengthening their bond further.
In this fanfiction, it could also be that Naruto is on a mission related to the battleship Yamato. There could be an evil force that wants to use the power of the Yamato for its own malicious purposes. Naruto has to team up with the ship's crew, which includes some characters with unique abilities of their own. They all work together, with Naruto leading the charge against the enemy using his Nine - Tails chakra and his vast array of ninja skills.
One possible plot could be that Naruto is on a difficult mission and Yamato is assigned to be his partner. They start off with some misunderstandings due to their different personalities. Yamato is more reserved while Naruto is brash. But as the mission progresses, Naruto starts to learn from Yamato's calm and calculated approach and Yamato begins to see Naruto's determination and heart. In the end, they form a strong bond and become great friends who can rely on each other in future battles.
Yamato might show his concern by constantly checking on Naruto's condition. He could be seen sitting by Naruto's bedside, feeling his forehead for fever regularly.
In the fanfiction, old man Naruto might be facing some sort of threat to the village again. He calls on Yamato, his old comrade, to help him. Together, they plan strategies and use their combined skills, with Naruto's nine - tails power (albeit in a more controlled and aged - related way) and Yamato's wood - style jutsu to protect the village one more time.
One possible plot could be that Yamato, with his calm and disciplined nature, instills in Naruto a better sense of self - control. Naruto might learn wood - style techniques earlier. He could also grow up with a stronger connection to nature due to Yamato's influence. For example, Naruto might be more in tune with the forest around Konoha and use it to his advantage during missions.
One possible plot development could be that his friends, like Sakura and Sasuke, come to take care of him. Sakura uses her medical skills to try and bring down his fever. Another could be Naruto having fever-induced dreams about his past, like his lonely days as a child. Maybe he even hallucinates about his parents. It could also lead to a situation where the village is in danger, but Naruto is too sick to help at first, creating a sense of tension and urgency among the other characters.
One possible plot could be that while they are sick, their comrades in Konoha come together to take care of them. Maybe Naruto brings them some of his favorite ramen, thinking it might cheer them up and help them get better.
In some fanfictions, when Naruto is sick and the Nine - Tails is involved, it could be a situation where the Nine - Tails' chakra is affected too. Maybe Naruto's illness weakens his control over the Nine - Tails' power, causing some unexpected leakage of chakra. This could attract the attention of enemies who sense the unusual chakra fluctuations.
In the fanfiction, Naruto Sensei's fever could be caused by overusing his chakra in a recent mission. As he lies sick, he might have flashbacks of his own training days when he was pushed to his limits. His friends like Sakura and Kakashi could come to check on him, and there could be some light - hearted moments as they recall old times while waiting for him to recover.
One possible plot could be that it's an alternate universe where Naruto and Tenten end up together in a situation that leads to pregnancy. Maybe they were on a mission together and some strange magic or jutsu affected them, causing Tenten to become pregnant. They then have to deal with the reactions of their friends and the challenges of impending parenthood.