Well, Naruto would be in a really tough spot. He loves his family and the village, and this situation would be a huge blow to his traditional values. He might struggle to understand how this happened between his son and Hinata. Hinata's family, on the other hand, would be protective of her. Her father would want to ensure that Boruto is taking responsibility. Boruto's friends would also be surprised. Some might be supportive, like Shikadai, who would try to see the good in the situation, while others might distance themselves at first, not sure how to handle this new and rather strange development.
Naruto would likely be excited. He loves his son so much that seeing different stories about Boruto would be like seeing different potential futures for him. He might even get some inspiration from the fanfiction to give Boruto some advice in real life.
Boruto might be in awe. He has always known his father as the Hokage, a powerful and respected figure. Seeing Naruto's past full of struggles, loneliness, and determination would make him realize how far his father has come. It could also make Boruto more empathetic towards Naruto and perhaps inspire him to be more like his father in some ways.
The villagers would likely be in shock. Naruto is a beloved figure, but killing his own son would be a very controversial act. Some might turn against Naruto, believing he has gone too far. Others might understand his reasons if they knew the full story, but still struggle with the morality of it.
Sakura could be really interesting. She might be confused at first by Menma's presence, thinking he's some kind of impostor Naruto. But as she gets to know him, she could see his unique qualities and might even develop a friendly rivalry with him. Another interesting character could be Kakashi. He would be observing Naruto and Menma's interactions closely, maybe even giving them some special training to help them work together better.
Some 'Menma Naruto' fanfictions focus on his relationship with his parents. For example, a story could be about how Menma tries to understand his father's legacy while dealing with his own identity crisis. It delves deep into his character and the complex world of Naruto's family.
One common theme is friendship. Since Naruto and Menma are often portrayed as having a special connection, their friendship is explored in many fanfictions. Another theme is power. How they develop their powers, use them together or compete with each other in terms of power is also frequently seen. Family is also a theme, as they both have complex family relationships in the Naruto universe.
There could be, but I would caution against seeking out 'lemon' fanfiction as it may not align with ethical or respectful consumption of media. Instead, consider exploring regular fanfictions that develop the characters of Menma and Hinata in a creative and meaningful way, such as their adventures together or how they support each other.