The plot could start with Spider - Man accidentally getting transported to Thanos' home planet. There, he has to survive and find a way back to Earth while being hunted by Thanos. As he evades Thanos, he learns about the weaknesses of Thanos' power and technology. When he finally gets back to Earth, he uses this knowledge to fight Thanos and protect the planet.
In a Spider - Man vs Thanos fanfiction battle, it's tough to say who would win. Spider - Man has his agility, spider - sense, and web - slinging abilities. He can quickly dodge attacks and come up with creative ways to fight. However, Thanos is incredibly powerful, with his strength and the Infinity Stones (if he has them in the fanfic). But if Spider - Man could somehow use his intelligence to outwit Thanos, like finding a weakness in his armor or the way he uses the Stones, he might have a chance. It really depends on how the author of the fanfiction writes the encounter.
In many fanfictions, Spider - Man can defeat Thanos by using his unique abilities. His agility and quick thinking give him an edge. He might use his web - slinging to disarm Thanos or outmaneuver him in combat.
It could be that the Iron Man's technology, which was used in the fight against Thanos, had some sort of hidden function. Spider - Man discovers this function while tinkering with the leftover tech. This function allows him to harness and concentrate a large amount of energy, similar to the power required for the snap. So, with his quick thinking and scientific knowledge, he figures out how to use it to snap Thanos out.
In fanfiction, Spider - Man's character development could lead to his victory over Thanos. He could grow in power and wisdom, learning from his past battles. His relationship with other characters might also play a role. For example, if he has a strong bond with Doctor Strange, they could combine their powers in a way that defeats Thanos. This would be a great exploration of character dynamics in the context of a fan - created story.
In certain comic arcs, Thanos has been responsible for Spider-Man's demise. However, the circumstances and details can vary depending on the specific comic series and plotlines.
Thanos could also win in a fanfiction. He has incredible strength and the power of the Infinity Stones at his disposal. In a lot of fanfictions, the power levels are often exaggerated. Thanos could simply use the Reality Stone to make Iron Man's weapons ineffective or use the Time Stone to freeze Iron Man in time and then defeat him. His brute strength alone is enough to overpower Iron Man in a direct confrontation. And his experience in battles across the universe gives him an advantage over Iron Man who mainly operates on Earth.
Another storyline could be that Thanos, aware of One Punch Man's power, tries to use the Infinity Stones to either eliminate him or make him an ally. There could be a long - drawn - out battle where One Punch Man has to constantly dodge Thanos' attacks while trying to find a way to land his one punch. In the end, he manages to do it and saves the day.