One common theme is the contrast between their powers. Hulk has raw strength and Spiderman has agility and webs. Fanfictions often play on how they can complement each other in battles.
One reason could be a misunderstanding. Maybe some villain has tricked Hulk into believing Spiderman is a threat. For example, the villain might have faked some evidence to make it seem like Spiderman was planning something bad against Hulk or his friends.
Their relationship could start as a simple partnership. They meet while fighting crime and gradually start to respect each other's abilities. As they work together more often, they become friends. For instance, Spiderman might initially be a bit intimidated by She - Hulk's strength, but as he sees her use it for good, he warms up to her.
One great Hulk x Spiderman fanfiction is 'The Unlikely Alliance'. It shows how the two superheroes, with their very different powers and personalities, team up to fight a common enemy. Their interactions are really interesting as Hulk's brute strength combines with Spiderman's agility and intelligence.
Well, in some fanfictions, Hulk might physically stand in front of Spiderman to shield him from attacks. For example, if there are powerful villains shooting energy blasts at Spiderman, Hulk's huge body can act as a barrier.
Spiderman's agility and web - slinging abilities could be combined with She - Hulk's super strength. For example, Spiderman could use his webs to create a net and She - Hulk could throw it with her great strength at enemies. Or Spiderman could swing She - Hulk around to gain more momentum for her attacks.
A frequent theme is the idea of mentorship. Sometimes Spiderman, with his intelligence and quick thinking, can act as a mentor to Hulk in terms of strategy, while Hulk can teach Spiderman about raw power and courage. Also, the theme of protecting the city from common threats is quite common. They have to put aside their differences and work together to keep New York safe.
One possible storyline could be that Spiderman and Red She - Hulk team up to fight a common enemy. Maybe a powerful villain has emerged in the city and their combined skills are needed to take it down. For example, a super - intelligent villain who has created a device that can disrupt all communication and power systems in the city. Spiderman's agility and web - slinging abilities along with Red She - Hulk's strength and durability would make for an exciting battle.
He might also use his webs to his advantage. He could try to web up Hulk's hands or feet to slow him down. Or he could create a web shield to block some of Hulk's attacks. For example, if Hulk throws a big rock at him, Spiderman could use his webs to create a net to stop the rock.
There could also be a plotline where they both enter a mysterious tournament. They have to fight other superheroes and villains in a series of battles. Along the way, they learn more about each other's capabilities and form a stronger bond.