Perhaps Anko is trapped in a genjutsu and Naruto uses his own experience with breaking free from illusions to save her. He could sense her distress and use his chakra to disrupt the genjutsu, freeing Anko. This would show Naruto's growth and his ability to help those in need, even a more experienced ninja like Anko.
One possibility is that Anko is poisoned during a mission. Naruto, having learned some medical ninjutsu from Tsunade, uses his skills to find an antidote and save her. He might have to search far and wide, facing various challenges along the way.
In a 'naruto saves anko' fanfiction, Naruto might find Anko in a dangerous situation like being trapped in a genjutsu by a rogue ninja. Naruto, with his strong will and Uzumaki chakra, could break the genjutsu and save her. He'd then comfort her and they might form a stronger bond, leading to Anko having more faith in the new generation of ninja.
In this fanfiction scenario, Naruto might save Anko from a dangerous training accident. Maybe Anko was attempting a very difficult jutsu during training and lost control. Naruto, with his quick reflexes and growing power, could sense the danger and rush in to protect her. He might use his Rasengan or some new techniques he has learned to counter the threat.
It could be a rogue ninja from Orochimaru's former experiments. This ninja might hold a grudge against Anko for betraying Orochimaru and decides to target her. Naruto would then have to face this powerful and vengeful enemy to save Anko.
Naruto's character could develop a sense of protectiveness towards Kurenai and Anko. He might become more mature in his decision - making, as saving them would require careful planning and not just brute force.
One possible scenario could be that the Anbu arrives just in time as Anko is about to use a dangerous jutsu on Naruto. The Anbu might use their superior speed and stealth to disarm Anko and rescue Naruto. Another scenario could be that the Anbu has been secretly observing Anko's actions towards Naruto, suspecting her of having some malicious intent. So they step in when they see Anko cornering Naruto. Maybe the Anbu uses some special ninjutsu to create a diversion and then whisks Naruto away to safety.
One challenge could be the reaction of the village. Since Naruto is a well - known figure, the news of him impregnating Anko might cause a stir. There could be rumors and gossip that they would have to deal with.
It could be that Anko is under some sort of mind - control in the fanfiction. And because of that, she attacks Naruto without really meaning to. Maybe she has been influenced by an enemy's genjutsu. So, she uses her powerful attacks on Naruto, and he gets hurt as a result.