A possible plot might involve Naruto being exposed to some ancient and powerful knowledge or artifact. This discovery gives him the means to 'destroy' bloodlines in the sense that he can change the very nature of chakra within a person. He might use this new - found ability to break the cycle of bloodline - based power hierarchies. He could start with the major clans like the Uchiha and Hyuga, and as he spreads his influence, the concept of bloodline superiority slowly crumbles, leading to a new era in the Naruto world where a person's worth is determined by their own efforts and skills rather than their bloodline.
Some secret organizations that have been manipulating bloodline abilities for their own gain could also be the antagonists. They would not want Naruto to disrupt their plans. They might send their most powerful agents to stop Naruto, leading to intense battles in the fanfic.
Well, it could start with Naruto seeing the dark side of bloodline powers being misused. So he decides to take matters into his own hands and develop a method to destroy bloodlines. This could lead to a huge rift in the ninja community, with some supporting him for trying to create equality and others opposing him because they value their unique family abilities.
It could also be that Naruto has been tricked. For instance, someone he trusts feeds him false information about the elemental nations being involved in a heinous conspiracy against him or his loved ones. This misinformation leads him to take drastic actions and start to destroy the elemental nations. Another idea is that Naruto loses control of his newfound and extremely powerful abilities. These abilities might be too much for him to handle and they end up causing destruction on a massive scale, starting with the elemental nations.
In the fanfic, Naruto might destroy the army in a very unique way. Instead of using his typical Rasengan or Shadow Clone Jutsu, he could discover a new power within himself. Maybe he unlocks a special form of Sage Mode that gives him the ability to control the elements in a completely different way, allowing him to take on the army with ease.
One possible plotline could be that Naruto has a sudden and extreme power-up that makes him overconfident. This overconfidence leads him to challenge Neji in a spar that gets out of hand and he ends up 'destroying' Neji in the sense of completely overpowering him. Maybe Naruto has unlocked a new form of his chakra that Neji can't counter with his Gentle Fist technique.
Maybe in this fanfic, Sasuke has gone too far in his quest for power and revenge. He starts attacking innocent people or trying to take over the Hidden Leaf Village. Naruto, as the hero, has no choice but to stop him. Naruto could use his talk - no - jutsu at first, but when that fails, he resorts to physical combat. He might start with his basic Rasengan and gradually level up his attacks as Sasuke counters with his Chidori and other powerful jutsus. In the end, Naruto destroys Sasuke's evil intentions and either kills him or imprisons him, depending on the tone of the fanfic.
There are countless Naruto fanfictions out there. For a 'Naruto destroys bloodline fanfic', it might involve Naruto challenging the traditional view of bloodlines in the Naruto universe. Maybe he discovers a way to nullify the advantages of certain bloodlines through his own unique abilities or some new form of jutsu he creates. However, without a more in - depth search on the major fanfic platforms, it's hard to give a definite example. You could start by looking at the most popular Naruto fanfics on these platforms and then dig deeper into their descriptions to see if they match what you're looking for.
One possible reason could be a threat to Konoha. If Iwa planned an attack on Konoha, Naruto, as a defender of his village, might take the fight to them and end up destroying parts of Iwa in the process.
It could be that Kiba has been involved in something that Naruto considers wrong. For example, if Kiba endangered the safety of the village or their friends, Naruto, being the protector - type, would take action against him. Or perhaps there was a misunderstanding between them. Kiba might have been framed for something, and Naruto, believing the false information, tries to 'destroy' Kiba in the heat of the moment.
The theme of justice might be present as well. If 'kina' is something evil or causing harm in the fanfic, Naruto's destruction of it can be seen as an act of justice. Also, the fanfic could explore the theme of sacrifice. Naruto might have to sacrifice something, like his time, energy or even relationships to be able to destroy 'kina' successfully.