It could be a plot twist if they get back together only to find out that there is a curse on their relationship. Every time they are happy together, something bad happens to someone they care about. They then have to decide if they are willing to sacrifice their own happiness to protect their loved ones or find a way to break the curse, which could lead to some really intense and emotional scenes in the fanfiction.
Perhaps a new character could be introduced who tries to come between them at first but actually ends up pushing them closer. This character might start dating one of them, making the other jealous. But then, they both realize that they are truly meant for each other through this complicated love triangle situation. As they work through their feelings of jealousy and confusion, they find their way back to each other.
A theme could be the reactions of their friends and family in the story to the pregnancy. This could add drama and different perspectives to the fanfic.
One possible plot twist could be that they get back together due to a common enemy. Maybe a new threat emerges in their world and they realize that they work better as a team when they are together. So they put aside their past differences and start to re - kindle their relationship.
One possible plot twist could be that when they go back in time, they accidentally change something that has a huge impact on their future relationships. For example, Naruto might unknowingly prevent Sasuke from leaving the village in the past, which could completely change how they interact in the present they return to. Another could be that they find out a hidden truth about their parents or the village's past that was covered up, like a secret alliance that their predecessors were involved in.
A really interesting plot twist could be that Steven goes back in time and discovers that the Diamonds had different motives than he originally thought. Maybe they were being influenced by some other force in the past, and by going back, he uncovers this mystery. Also, he could find out that some of the things he thought were his friends' ideas were actually planted by an outside source long ago. This would completely change his understanding of the relationships and history in the Steven Universe world.
One possible plot twist could be that Ragna discovers he is the cause of a major historical event that he previously thought was just a part of history. For example, he might find out that his actions in the past led to the rise or fall of a powerful kingdom.
A really cool fanfiction could be set in a modern day reboot of their story. Tate and Violet are reincarnated in a different time, but still have a connection. They start to remember their past lives slowly as they are drawn to each other in this new world. They have to deal with modern problems while also coming to terms with their haunted pasts.
One common theme could be the reactions of the other characters to Violet Tate's pregnancy. For example, her friends and family might have different emotions, from shock to joy.
Well, perhaps a plot twist could be that when Kirito goes back in time, he discovers that his own existence in the past was a key factor in creating the problems he faced in the future. So, he has to figure out a way to change things without erasing himself. Or, he could go back and find that the person he loves in his original timeline has a completely different personality or role in the past, which throws him off and makes his feelings really complicated.
I'm not sure if there is a specific 'Tate Violet pregnant fanfic' available. Fanfics can be quite diverse and spread across various platforms. You might want to check popular fanfic websites like Archive of Our Own or Fanfiction.net and search for it there.