Well, it could be about Mikoto seeing Naruto's lonely situation and deciding to take him in. Maybe she'd teach him some Uchiha techniques and help him grow stronger. She could also introduce him to Sasuke as a brother figure, changing the whole dynamic between Naruto and Sasuke in the Naruto world.
In such a fanfiction, it could be a story full of new possibilities. Mikoto Uchiha, with her kind heart, might offer Naruto the family he always desired. She could teach him some Uchiha techniques secretly, which would make Naruto even more powerful and unique in the ninja world.
Naruto's life would experience a significant shift. With Mikoto Uchiha adopting him, he would be exposed to the Uchiha way of life. He might get to learn about the clan's traditions, which could shape his character in new ways. His living situation would improve, as he'd be in a more stable family environment. In terms of his ninja development, Mikoto could pass on some of her own knowledge or connect him with other Uchiha members who could help him train. This could lead to Naruto having a more diverse set of skills and a different perspective on the ninja world compared to his original story.
No, it's probably not popular. A good Naruto fanfic usually has a title that is both appealing and in line with the values of the Naruto community. This title contains a derogatory word which would likely turn off many readers, so it's not likely to gain much popularity.
The child could be an orphan from a small, destroyed village that Naruto comes across during one of his missions. This child might have lost their family to a powerful enemy and Naruto feels a sense of responsibility to take them in.
One idea could be that Mikoto discovers baby Naruto alone and decides to take him in and protect him, raising him alongside Sasuke. This could lead to a very different dynamic in the Uchiha clan and Naruto's growth.
A 'naruto mikoto lemon fanfic' often has a blend of the Naruto universe's elements with the relationship between Naruto and Mikoto. The fanfic may include the use of jutsus, ninja clans, and the overall world - building of Naruto. Regarding the 'lemon' part, it usually means there will be some level of romantic or sensual undertones, which could be used to develop the emotional connection between the two characters. However, different authors will have different takes on how much and how they portray this aspect.
One idea could be a story about Kushina and Mikoto being friends when they were young and how their friendship influenced Naruto's life. For example, they could have made a pact to always look out for each other's children. Kushina might have told Mikoto some special Uzumaki techniques that Mikoto then passed on to Sasuke in a way. Another idea is a time - travel fanfic where Naruto goes back in time and meets his mother Kushina and Mikoto when they were in their prime. He could learn a lot about the past of the village and his family from them directly.
Since the title seems a bit unorthodox, it's hard to tell precisely. But if we assume it's a regular Naruto fanfic with Mikoto in it, it might explore aspects of Mikoto's character that were not fully explored in the original Naruto series. It could be about her backstory, her relationships with other characters, or her role in some new plotline within the Naruto world.