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.
Maybe in the fanfiction, there's a new enemy that targets the old - timers like Naruto and Yamato because of their past achievements. They are forced to come out of retirement and use their rusty but still formidable skills to defend themselves and the village. They might also have to train some inexperienced shinobi along the way to help in the fight.
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.
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.
Perhaps the story could focus on Old Man Naruto's relationship with Yamhoto. They could be reminiscing about their adventures together. Yamhoto might be facing some sort of trouble, and Naruto, despite his old age, decides to help him out, showing his loyalty and friendship.
Well, it could be about Naruto having some sort of special connection with the old man of the mountain. Maybe he discovers some ancient power or knowledge related to it. For example, the old man of the mountain might teach Naruto a unique jutsu or give him a task that will change the course of the ninja world.
I'm not entirely sure specifically as 'lemon' in fanfiction often implies some sort of romantic or slightly risqué content which may vary greatly. It could potentially be about an older male character in Naruto in some sort of unusual or unique relationship scenario, but without reading it, it's hard to say for sure.
A simple way is to have Yamato train Naruto in katana - wielding techniques. Since Yamato is a skilled ninja, he could teach Naruto how to handle a katana, which Naruto might initially resist as he's more used to his own combat style. But as he learns, he discovers new ways to combine his ninjutsu with katana - based attacks.
A great 'Naruto has Yamato' fanfiction could be set in an alternate universe where Yamato is Naruto's main mentor instead of Kakashi. This would lead to a completely different Naruto in terms of his skills and how he approaches challenges. Yamato's ability to understand and control the Nine - Tails' chakra within Naruto could be explored more deeply, resulting in Naruto having better control over his power much earlier in the story.
He could also interact with the new generation of ninjas in his own village who might see him as a relic of the past at first. But as they get to know him, they learn valuable lessons from his experiences. He could train them in unique ways that combine his old - school ninja techniques with the new knowledge and abilities that the new generation has developed.