Perhaps it's a wish gone wrong. She makes a desperate wish for a change and gets this unexpected transformation. Now she has to navigate life in a completely different way.
It could be a scientific experiment gone haywire. Some crazy scientist's concoction transforms her gender. And then there's all the drama of her dealing with the new body and society's reactions.
One possible scenario is that they are friends just having a good time, like shopping together or going to a concert. Another could be that they are colleagues discussing work - related matters outside the office. And of course, they could be a couple on a date, enjoying each other's company in public places.
It could be a survival situation in a post-apocalyptic world. Maybe resources are scarce and people are forced to fight for them.
One possible reason could be a magical or supernatural curse. Maybe he offended a powerful witch or wizard who cast a spell on him. Another reason could be some sort of scientific experiment gone wrong. For example, if he was part of a secret experiment involving hormones or genetic manipulation, and things didn't go as planned.
Another theme might be identity. His identity as a man is completely shaken when he turns into a pregnant woman. He has to re - evaluate who he is, his gender role, and how society views him. It could be about breaking gender norms and exploring the fluidity of identity.
One possible scenario could be in a social or work setting. Maybe someone spreads a false lesbian story about her to damage her reputation. For example, if she is up for a promotion at work, a jealous colleague might spread a story that she had a lesbian relationship which could be seen in a negative light in a conservative work environment.
One reason could be a curse. Maybe she offended a powerful witch or magician, and as a punishment, she was turned into a mannequin. Another reason might be a deal with the devil - like figure. She made a Faustian bargain and the price was her transformation.
One possible scenario could be that Peter Parker's closest friends find out his identity in a moment of danger. For example, when they are all facing a powerful villain together and Peter has no choice but to unmask to save them.
One possible plot could be a curse placed upon him by an evil sorcerer. Maybe he offended the sorcerer in some way, and as revenge, the sorcerer uses dark magic to transform him into a woman. He then has to deal with all the new physical and social aspects of being a woman while trying to find a way to break the curse.
It might be a science - fiction story. There could be some kind of experiment gone wrong. Scientists are working on a new genetic technology to allow men to carry babies in the future. But a malfunction in the experiment causes one man to suddenly start showing signs of pregnancy, and he has to deal with the shock and the implications for his life and relationships.
In this fanfiction, it could be that a powerful enemy from another dimension arrives. This enemy has the ability to turn living beings into weapons. They see Naruto as a prime target because of his strong chakra. Once turned into a weapon, Naruto might be used to break through the defenses of Konoha. His friends then have to find a way to reverse the transformation, which could involve a long and dangerous journey to find a special antidote or a powerful jutsu.