First, make sure you understand the basic premise of the 'son of gato' story or the original work it's based on. This will help you better understand the fanfictions. Second, read reviews if available. Other readers' opinions can give you an idea of whether the fanfiction is well - written or not.
I don't know who created 'el gato secret story' as there's not enough information given. It could be an independent author or a small publishing house.
Since we don't have much information about 'el gato secret story', it could be a variety of things. It might be a children's story, in which case the secret could be something simple and innocent like the cat's favorite hiding spot in the garden. Or it could be a more complex story for an older audience, perhaps involving a mystery that the cat is trying to solve, or a secret that has to do with the cat's past or its family. It could also be a cultural story specific to a certain region where cats hold a particular significance and the secret is related to that cultural meaning.
Another option could be Wattpad. Although it has a wide range of content, not all of it is strictly fanfiction. But it's still worth a search. Look for groups or communities on Wattpad that are dedicated to the same fandom as 'son of gato' and ask around if anyone knows where to find relevant fanfictions.
In a 'Naruto kills Gato' fanfiction, the plot could start with Gato's continued oppression in the Land of Waves. Naruto, having witnessed the suffering of the villagers, decides he's had enough. He uses his Shadow Clone Jutsu to surround Gato and his men. With a swift combination of Rasengan and his ninja skills, he takes Gato by surprise and defeats him, thus liberating the Land of Waves in a more direct and violent way compared to the original story.
Naruto could use his improved taijutsu skills. He might close in on Gato quickly and land a series of powerful punches and kicks that Gato can't defend against. Since Naruto is quite fast and has good reflexes, he could easily overwhelm Gato in close - combat.
Well, one possible plot could be that Gato has some new evil plan in the Land of Waves. Naruto, having grown stronger, decides he can't let Gato harm the innocent people there anymore. He uses his new jutsu and his quick thinking to outwit Gato's men first. Then, in a final showdown, Naruto unleashes a powerful Rasengan, directly hitting Gato and killing him, thus saving the Land of Waves from Gato's tyranny.
The villagers of the Land of Waves would surely support Naruto. They have suffered a great deal under Gato's rule, so they would see Naruto as their savior. Also, Sasuke might support Naruto. Even though they have their differences, Sasuke would recognize the need to stop someone as evil as Gato.
There could be a power vacuum left by Adaly White's death. This might lead to different factions in the Gato base area vying for control. Naruto may then have to deal with the aftermath and ensure that a more just leadership takes over.
It could be that Naruto has some sort of intel about Adaly White's weakness. He uses this knowledge to his advantage in the Gato base. He might first disable any guards or traps around Adaly White and then use his chakra - enhanced strength to land a fatal blow.