If Ben entered the Attack on Titan world, his relationships would be complex. He might initially be seen as a threat, but as he uses his powers to help, he'd gain allies. His relationship with Eren could be one of mutual respect as they both have powers to fight. Eren might be in awe of Ben's ability to transform into different forms.
The characters' relationships would be very different. For example, Mikasa might be initially distrustful of Ben but come to see him as a valuable asset. Ben, on the other hand, might befriend Armin because of his intelligence. His relationships would also depend on how his alien forms are perceived. If he uses some of the more monstrous - looking forms, it could cause fear at first. But as they see he's on their side, new bonds would form. And there could be rivalries too, like between some of the more prideful Survey Corps members and Ben when it comes to combat strategies.
The world of Attack on Titan would experience a major transformation with the introduction of Pokemon. Socially, the relationship between people would change as they bond over their Pokemon. There could be Pokemon centers and Pokemarts within the walls. Economically, a new industry would emerge around Pokemon. In terms of combat, as I mentioned before, different types of Pokemon would bring new tactics. Fire - type Pokemon could set the Titans on fire, ice - type Pokemon could freeze them, and so on. Also, the idea of Pokemon evolution could be incorporated into the story. Maybe the more a trainer and their Pokemon fight Titans together, the stronger their bond and the more evolved their Pokemon becomes, making them even more effective against the Titans.
The 'Attack on Titan' characters would be quite shocked by the technology and the general chaos in the 'Gintama' world. Characters like Armin would be very interested in all the strange inventions and the way society functions in 'Gintama'. He might try to understand the economic and political systems there. And the 'Gintama' characters would be in awe of the 'Attack on Titan' characters' ability to fight Titans. They could team up to face common enemies or just have a series of comical misunderstandings that lead to all sorts of adventures.
Well, in this crossover, the Survey Corps members like Armin would be fascinated by the intelligence of some ghouls. They might try to communicate with them to gain knowledge about their powers. Ghouls like Touka would be in a difficult situation. She would be in a world full of titans, which are much larger and more difficult to deal with than the CCG in her own world. She might have to learn new fighting techniques from the Survey Corps. And characters like Erwin would see the ghouls as a valuable asset, trying to recruit them to fight the titans.
In a crossover, the relationships would be a complex mix. Consider a 'Twilight' werewolf in the 'Heroes' world. They might find kinship with characters who have animal - like powers. But at the same time, their territorial nature could cause conflicts. On the other side, if a 'Heroes' character with healing powers went to the 'Twilight' world, they could potentially change the fate of some characters. This would have a huge impact on the relationships within the 'Twilight' universe, especially for those whose lives are in danger, like some of the human characters in the vampire - werewolf conflict.
Eren could be really inquisitive about the Transformers' powers. He might try to learn from them how to better use his Titan - shifting abilities. The Autobots, like Bumblebee, would be friendly and try to communicate with the humans in their own way, which could be a bit difficult at first but they would manage.
The Survey Corps' ODM gear could be used in new and creative ways in a crossover. They could use it to quickly move around the Tokyo Ghoul cityscape, giving them an advantage against the ghouls. Meanwhile, the ghouls' kagune could be used to attack Titans in ways the Attack on Titan characters haven't seen before. For example, a ghoul could use its kagune to slice through a Titan's nape from a distance.
Luffy would probably be really excited to meet the Survey Corps. He'd see them as cool warriors and want to team up right away. He might even try to convince them to join his crew. Eren, on the other hand, would be a bit more suspicious. He's used to a world full of danger and betrayal, so he might not trust the Straw Hat crew immediately. But as he sees their loyalty to each other, he could start to warm up to them.
The characters from 'Attack on Titan' would have a mixed reaction to the 'Titanfall' technology. Some, like Armin, would be very interested in understanding how it all works. He would study the technology and come up with new strategies for using it against the Titans. Others might be more hesitant. Levi, for instance, might be skeptical at first but would eventually see the value. They would need to adapt to things like the energy systems, which are very different from what they are used to. They would also have to learn new combat maneuvers that are designed around the 'Titanfall' technology.
If there was a crossover with the Spider - Man universe. Peter Parker would be in awe of Wanda's powers. He would probably try to ask her a million questions. This could make Vision a bit jealous as he sees Peter as a bit of a pest. Meanwhile, Aunt May would probably invite Wanda and Vision over for dinner, and in that domestic setting, we would see a whole new side of their relationships. Wanda might start to see Vision in a more human way as she observes the relationship between Peter and Aunt May.
For the female characters, Sakura could potentially form a friendship with Mikasa. They are both strong and independent. Sakura's medical skills could be of great use in the world of Attack on Titan, where injuries are common. Mikasa might teach Sakura some of her combat skills in return. As for the male characters, Kakashi could mentor some of the younger members of the Survey Corps, sharing his wisdom and combat experience.