Well, it could be about Naruto having to face the loneliness of being the last. Maybe he has to carry on the traditions and values of his village all by himself. He might struggle with the weight of everyone's expectations and also deal with the memories of those he's lost.
It could be the remnants of old enemy clans who see Naruto as the last obstacle to their full control. For example, some rogue members of the Orochimaru - inspired groups might want to capture Naruto to extract his unique abilities since he's the last of his kind.
One possible plot could be that Naruto and Temari team up for a crucial mission to save the ninja world from a new, powerful threat. They start off as reluctant partners but gradually learn to trust and rely on each other, leading to a deep friendship or even a romantic relationship by the end.
Well, it might be about Naruto somehow ending up in the Star Wars universe and being the last Jedi. Maybe he uses his ninja skills combined with Jedi powers to fight against the Sith or some new dark force.
Well, the plot could be that Naruto is the sole survivor after some kind of apocalyptic event. Maybe all the other shinobi were wiped out by a powerful enemy or a deadly disease. Naruto then has to find a way to rebuild the world while also dealing with his loneliness and the memories of his lost friends.
Perhaps it's a story of their adventures after the events of 'The Last'. They could go on a journey to explore some hidden parts of the ninja world. Along the way, they might encounter old enemies who have new motives or discover new jutsu. Hinata could also be further developing her own skills, and Naruto is there to support her as she grows stronger. Their relationship would deepen during this time as they face different situations together.
I'm not entirely sure as 'lemon' in fanfiction often implies inappropriate content. But if we assume it's a normal fic, perhaps it could be about Naruto being the last male in a world facing some kind of gender - imbalance catastrophe. He might have to take on the responsibility of repopulating the world in a non - vulgar way, like through some kind of genetic research or finding a way to reverse the situation that led to this imbalance.
Well, it could be a story where the ninjas from Naruto learn about bending in the Avatar world. They might be initially confused but then start to adapt. Naruto himself could try to learn airbending, given his fast - moving and free - spirited nature. And there could be a conflict where the shinobi way and the bender's philosophy clash, leading to interesting character developments.
Maybe the last male character is an outcast in the village. But as the story unfolds, he finds out that he has a special connection to an ancient prophecy. This connection makes him the key to saving the ninja world from a great darkness that is slowly spreading. He has to overcome his own insecurities and the distrust of his fellow villagers to fulfill his role in the prophecy.
It could be a rogue ninja who has developed a new and extremely deadly jutsu. This ninja has a vendetta against Konoha and was able to take out most of the ninja there, leaving Naruto as the lone survivor.
One idea could be the lone survivor Naruto having to navigate a world where all his friends have been put under a powerful genjutsu. He has to find a way to break the spell alone, facing many hidden enemies along the way.