I'm not sure as I haven't read this specific fanfiction. It could potentially involve Tris being in some sort of danger from Peter, and 'four' (presumably a character) coming to her rescue. Maybe Peter has some malicious intentions towards Tris, like trying to harm her or get her into trouble, and Four steps in to prevent that.
In the fanfiction 'four saves tris from peter', the most prominent characters are Four, Tris, and Peter. Four is likely to be a brave and capable character, with qualities that enable him to rescue Tris. Tris is probably a character in need of help, perhaps she's in a weak or dangerous position. Peter, on the other hand, seems to be the source of trouble, the one who poses a threat to Tris, which prompts Four to take action.
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.
In the fanfiction, Tobias might save Tris from Peter by using his physical strength and combat skills. He could have jumped in just as Peter was about to harm Tris, overpowering Peter and getting Tris to safety. Maybe he used his knowledge of the area to find a hiding place for Tris away from Peter's reach.
In this type of fanfiction, it could be a really interesting scenario. Four might be nervous when meeting Tris' parents. Maybe he'd try to impress them with his skills and strength. He could be worried about living up to their expectations for Tris' partner.
In the fanfiction, the pregnancy could be a catalyst for them to re - evaluate their relationship. They might realize how much they truly mean to each other. Four could be more open about his feelings, and Tris could let her guard down more. They could also start planning for their family, which includes discussing things like where they will live, how they will raise the child, and what values they want to instill. This would involve a lot of heart - to - heart conversations and a deepening of their emotional connection.
Love could be a strong motive. If Tobias has feelings for Tris, he would naturally want to protect her from harm, especially from someone like Peter who might be a bully or a threat.
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.
Trust is a big theme. Since they start off on rather rocky terms, fanfictions often focus on how they build or break trust. Also, the theme of self - discovery is common. As they interact more, both Peter and Tris learn more about themselves and their capabilities.
Well, I'm not sure specifically about 'peter x tris pregnant' fanfiction. However, in general, when looking for a particular type of fanfiction, it's a good idea to check fanfiction forums as well. Sometimes fans discuss and recommend specific stories there. Also, make sure to read the reviews if you find any stories, as they can give you an idea of whether it's worth reading or not.