One possible motivation could be a misdirected sense of revenge. Maybe Naruto is tricked into believing that Iruka has done something unforgivable against Konoha or someone he loves. But this would require a huge distortion of the characters' personalities.
In the Naruto universe, Naruto killing Iruka would be a huge deviation from the norm. Maybe in this fanfiction, the author is trying to show how much Naruto has changed due to some extreme circumstances, like being possessed by an evil force. However, it's still hard to imagine as Naruto's bond with Iruka is one of the fundamental positive relationships in the show.
One scenario could be when some villagers start to be mean to Naruto. Iruka steps in and scolds them, telling them Naruto is just a kid. Another could be during a training exercise that gets a bit too dangerous for Naruto, and Iruka quickly intervenes.
It also improves Naruto's skills a great deal. He becomes better at combat and using his ninja techniques. For example, his Rasengan might be more powerful or more easily controllable after Iruka's training. Moreover, Naruto's confidence grows under Iruka's guidance. He no longer doubts himself as much and is more willing to take on challenges.
Physically, Iruka takes care of Naruto's symptoms. If Naruto has a cough, Iruka might make him herbal tea to soothe his throat. If Naruto has a fever, he uses cold compresses to bring the temperature down. He monitors Naruto's condition closely and adjusts his care accordingly, making sure Naruto is on the road to recovery as quickly as possible.
At first, it might start with Iruka showing simple kindness to Naruto, like making sure he has enough to eat. As time goes on, Naruto starts to see Iruka as a father figure. He looks up to Iruka and wants to make him proud.
Well, in the fanfiction, Iruka may be protective by constantly checking on Naruto's well - being. He could ensure Naruto has enough to eat, is getting proper training, and is not being bullied by other villagers. He might also be protective in the sense that he gives Naruto extra attention and guidance in his ninja training, more so than he would for other students.
Initially, Naruto might be a bit hesitant to fully embrace this new family situation. But Iruka's kindness and Anko's enthusiasm would gradually break down his walls. Iruka would continue to be Naruto's academic and moral guide, as he always has been. Anko would introduce Naruto to a more carefree and adventurous side of life. They would have family outings, training sessions together. As Naruto grows, he would start to understand the value of having them in his life, and they would be proud of his every achievement, forging a deep and loving bond.
Iruka influences Naruto's early development by being a positive role model. Naruto looks up to Iruka and wants to be like him. Iruka's kindness and belief in Naruto give Naruto the confidence to start believing in himself.
One common theme is the idea of family. Since Naruto lacks a traditional family, Iruka often becomes a father - like figure in fanfiction. So, the theme of family and the bond that develops between them is quite popular.