There are fanfictions where Shinji Ikari has different relationships with the other characters. In some, he forms a closer bond with Asuka earlier on and they work together more effectively against the Angels. This changes the whole dynamic of the story as their combined strength and new - found friendship alters the course of events.
One idea could be that Shinji Ikari is transferred to the Highschool DxD school as an exchange student. He might initially struggle with the very different supernatural environment compared to his Evangelion world. His experiences with Angels could give him a unique perspective on the devils and other beings in the Highschool DxD world, leading to some interesting interactions and storylines.
One idea could be a crossover with a superhero universe. Shinji Ikari could gain superpowers and have to navigate the complex world of superheroes, dealing with their moral codes. Another could be a crossover with a fantasy world like Middle - earth. He might find himself on a quest with hobbits or elves. A third idea is a crossover with a post - apocalyptic world, where Shinji's experiences in his own apocalyptic - like setting of Neon Genesis Evangelion could be put to use in a different kind of desolate landscape.
First, understand Shinji's character well. He is a complex and often troubled character. Know his insecurities, his relationships with others like Misato, Asuka, and Rei. Then, come up with a unique plot. It could be a what - if scenario, like what if Shinji was the first to fully understand the true nature of the Angels?
First, you need to have a clear idea of the other universe or story you want to cross over with. If it's a well - known one, study its lore, characters, and settings. Then, think about how Shinji Ikari would fit into that world. What would his role be? For example, if it's a magical world, would he be a reluctant hero or a confused outsider? Next, plan out the basic plot. How will the two worlds collide? And finally, start writing, don't worry too much about making it perfect at first.
He could also become more social. In the Highschool DxD world, there are many different species and characters to interact with. Shinji, who is often isolated in Evangelion, might start to open up and form friendships or alliances. This would be a big change from his usually withdrawn personality.