One common theme could be the challenges they face as a couple during the pregnancy. It might include things like dealing with their different personalities while preparing for a new life together.
Well, I'm not sure of specific 'eric and tris pregnant fanfiction' stories off the top of my head. But you could try searching on fanfiction - dedicated websites. They usually have a wide range of stories based on different themes, and you might find some there.
Eric might also use his position of authority. If he's in a position of power within the story's setting, he could simply order Peter to stop. For example, if Peter is violating some rules of the group or faction they belong to, Eric could threaten him with punishment if he doesn't let Tris go.
A theme that can't be ignored is the transformation. Sometimes Tris undergoes a transformation, either physically or in terms of her understanding of the world. It could be that she becomes more like a vampire or gains a new perspective on life. And the overarching theme of good vs. evil, with Eric and Tris often on the side of good, fighting against the more malevolent vampires or entities in the fanfiction.
One common theme is the exploration of forbidden love. Since Eric has a rather antagonistic role in the original story, the idea of him and Tris getting together goes against the norm. Another theme is redemption. Eric might be seen as trying to redeem himself in Tris's eyes. And there's also the theme of power dynamics as they both come from different positions of power within the factions.
One common theme could be conflict. Since Eric is hurting Tris, there would be the obvious physical or emotional conflict between them. This can create a lot of tension in the story.
I'm not sure about specific 'eric hurts tris fanfiction' works off the top of my head. But you can try searching on fanfiction websites like Archive of Our Own. There are usually a lot of fan - created stories in different genres and themes related to various characters.
There's also 'Eric and Tris: Blood Bond'. In this fanfiction, the author creates a unique vampire world. Tris is a human who gets caught up in the vampire politics because of her connection to Eric. It's a long read but worth it as it delves deep into their characters and the vampire society they are a part of.
Eric might also see Tris as an asset to his own plans or goals. If he wants to gain more power or influence within their community, he might think that by saving Tris from Peter, he can earn her loyalty and have her on his side. And Tris is known for her strong will and skills, which can be useful to Eric.
Well, 'Hidden Feelings: Eric x Tris' is also great. It explores the idea that Eric and Tris have hidden feelings for each other that they are reluctant to admit. The author does a wonderful job of building up the tension between them and gradually revealing their true emotions through various events in the story.