One possible scenario in this fanfiction could be that the pregnant fan has been a huge One Direction supporter for years. When she discovers she's pregnant, she's going through a tough time financially and emotionally. Niall, being the kind - hearted person he is in the fan's imagination, gets to know about her situation and steps in to help. He could provide resources for her pregnancy, like getting her in touch with good doctors or helping her with baby - related expenses.
Well, in such a fanfiction, it could explore the unique relationship between Niall and the pregnant fan. Maybe it starts with the fan meeting Niall at a concert and later finding out she's pregnant. The story might then revolve around how Niall offers support and friendship, perhaps even inspiring her through the pregnancy journey.
In this fanfiction, the pregnant fan might write to Niall about her situation. Niall, who values his fans deeply, decides to meet her. Their meeting could be filled with emotions. As time goes on, the fanfiction could show how the fan's pregnancy progresses and how Niall's presence in her life, even if just in a fictional sense, gives her the strength to face the challenges of motherhood. It could also touch on how the other members of One Direction might react to Niall's involvement with this fan.