One possible plot could be that Naruto and Anko have a series of unexpected encounters. Maybe they are on a mission together and during some dangerous situations, they grow closer. Their relationship gradually develops from friendship to something more. Eventually, Anko discovers she is pregnant and they have to face the reactions of their friends and the ninja community.
He might also become more reserved in future relationships. After being cheated on by Anko, Naruto could be more cautious when it comes to getting close to someone again, always having that fear in the back of his mind that he could be betrayed once more.
Well, one possibility could be that Naruto is in a really tough battle, perhaps against a group of powerful enemies. Anko could show up just in time. She might use her snake-based jutsu to fend off the attackers. For example, she could summon snakes to entangle the enemies, giving Naruto a chance to catch his breath and regain his strength.
Yes, there are likely some 'Naruto Gets Pregnant' fanfictions out there in the vast world of fan - created content. However, such concepts often deviate from the original source material in very extreme ways.
Anko might start off as just a savior. But after saving Naruto, she could become more protective. Her tough exterior might soften a bit as she realizes Naruto's importance not just to the village but also to her on a personal level.
In this fanfiction scenario, Naruto might seek advice from his friends. Sasuke could be rather cynical about it, saying something like 'I knew she wasn't trustworthy.' While Sakura might be more empathetic and try to comfort Naruto. Naruto could also start to have flashbacks of his relationship with Anko and notice all the signs he missed that indicated she was cheating.
Maybe Naruto is trapped in a dangerous place, like a collapsing cave during a mission. Anko, with her quick thinking and combat skills, and Kurenai, who is very strategic, find him. Anko could break through any physical barriers in the cave, and Kurenai would use her genjutsu to keep Naruto calm so he doesn't panic and make the situation worse. Together, they get him out of there.
Sakura might be initially shocked and a bit jealous, but she would probably come around to support Naruto as a friend. Kakashi would be more of a calm and collected figure, offering advice on how to handle the situation both as a ninja and as an expecting father. Sasuke, on the other hand, might be indifferent at first but later show some concern for Naruto's well - being in this new situation.
I'm not sure if there is such a specific fanfiction. Fanfiction can cover a wide range of very creative and sometimes out - of - the - ordinary ideas, but this one seems rather unusual. You might try searching on some large fanfiction websites to see if it exists.
I'm not sure if there is a single 'popular' one in the sense that it's widely known. Fanfiction is a vast world with so many different stories. Some people might write this type of fanfiction for the shock value or to explore a different relationship dynamic. But it's likely that most Naruto fans are more focused on the canon pairings or more established fan - created pairings. So it might be a bit of a niche within the Naruto fanfiction community.