It could be a new character introduced in the fanfic. Maybe a wandering ninja who was also on a similar mission and they teamed up. During their time together, they fell in love and he's the father.
There's a possibility that it's one of her comrades. For example, Rock Lee. He has always been very passionate and has a deep respect for Tenten. Maybe during the mission, their relationship took a different turn and he could be the father. However, this would be a big change from their normal friendship dynamic in the original Naruto series.
Another option could be an enemy turned ally during the mission. They start off as adversaries but as they face challenges together, they develop feelings for each other. He might be from a different ninja village, which would add more drama to the story as their relationship would be complicated by the politics between their respective villages.
In the fanfic, after the mission, Tenten could have been exposed to a unique chakra or a special artifact. This exposure somehow affects her body in a way that results in pregnancy. The story could revolve around her search for answers. She might go on a journey to find out what exactly happened to her. Along the way, she could encounter old friends and foes alike. And as she gets closer to the truth, she also has to deal with the physical and emotional changes that come with pregnancy in a world full of ninja battles and political intrigue.
I haven't come across a 'naruto gets tenten pregnant fanfic' specifically. Naruto fanfics typically revolve around the established storylines and characters' development within the framework of the ninja world. This kind of plot seems a bit out of the ordinary for the Naruto fandom. Maybe if you search on some more niche or adult - oriented fanfic platforms (though I don't recommend those), you might find something, but it's not likely to be a widespread or well - known fanfic.
Maybe Rock Lee. He has always been very passionate and his positive energy could have attracted Tenten. Their friendship might have blossomed into a romantic relationship, resulting in her pregnancy.
Maybe it's a completely new character introduced in the fanfiction. This new character could have some special powers or a unique connection to Naruto that results in the pregnancy.
Or, in a more creative take, it could be a new character introduced just for this fanfic. This new character could bring a whole new set of dynamics and storylines, like a mysterious stranger who has some special connection to Clary.
Most likely, Percy could be the father. They have a strong relationship in the original series, so it would be a natural choice. Their chemistry and shared adventures could be the basis for a story where they start a family together.
It could be her long - time love interest. In many fanfics, the most obvious choice would be the character she has the strongest romantic connection with in the original series.
Neji could be a potential father. Their long - standing friendship and mutual respect could have developed into a deeper relationship over time, leading to the pregnancy.
A common choice could be Sasuke. Given their long - standing relationship and connection in the original series, it would make sense for him to be the father. Their relationship has always been complex and a pregnancy would add another layer of depth to it.
If such a fanfic existed, it would probably start with some kind of unexpected encounter or relationship development between Naruto and Tenten. Then, the discovery of the pregnancy would bring a whole new set of problems. They would have to face the reactions of their friends, like Sakura and Kakashi. Naruto might also struggle with his duties as a ninja while trying to be there for Tenten and the unborn child. And Tenten would have to deal with the physical and emotional changes during pregnancy in the context of being a ninja in a dangerous world.