Perhaps in the 'harry gives birth at dursleys fanfiction', there's a new form of magic introduced. Harry could have been affected by a magical experiment that causes this strange phenomenon. The Dursleys, who have always mistreated Harry, now have to face the consequences of having such a unique and unheard - of event happening in their house. They might be in a state of panic and confusion as they try to figure out what to do.
It could be some other wizard who Harry had an unexpected encounter with. Maybe it was a wizard who was secretly in love with Harry and used some sort of love - related magic that had an unforeseen consequence.
Perhaps the 'bro' is a place that has some special properties. Harry enters this 'bro' place, and due to the energy or magic there, he undergoes a transformation that leads to giving birth. The story could then be about Harry coming to terms with this new situation, dealing with the physical and emotional changes, and trying to find out how to reverse it or at least live with it.
Well, one possibility could be that the Dursleys suddenly realize Harry's importance and the power he holds. They might see how he could bring them some sort of status or protection in the wizarding world. So, they start to accept him, change their attitude towards him, and perhaps even help him in his magical studies in secret.
In some interpretations, it could be that Harry finally snaps after years of abuse from the Dursleys. Maybe they pushed him too far one day and in a fit of rage, he uses his magic to end their lives. It's a very dark and extreme take on the Harry Potter universe.
One possible plot could be that Snape discovers he has a unique magical ability that allows him to carry a child. He might keep it a secret from everyone in Hogwarts due to fear of ridicule. As he nears the time of giving birth, he would have to find a secluded place within the castle or in the Forbidden Forest. He would endure the pain alone, using his own potions and magic to ease the process as much as possible.
The plot could also involve the father of the baby being a mysterious figure. Maybe he's from a far - off land that Elsa visited during her adventures after the events of the Frozen movies. And as she gives birth, the baby could inherit some of her ice powers, which would lead to a whole new set of challenges and adventures for Elsa as a mother, like teaching the baby to control its powers from a very young age.
One possible plot could be that Sakura has a difficult birth. Naruto is by her side, worried sick. Their friends from the village are also there, waiting anxiously. Maybe there are some complications during the birth, and Sakura has to draw on her inner strength as a kunoichi. And in the end, she gives birth to a healthy baby, which brings great joy to the whole village.
Perhaps it could involve some sort of magical or scientific experiment gone wrong that results in Tony being able to give birth. Peter could be the result of a genetic manipulation within Tony's body, and the story might then focus on how they adapt to this strange new situation.
Perhaps the fanfiction focuses on how the baby changes the relationships in Naruto's life. Her relationship with Sasuke could be affected, whether they are friends or something more. The baby could also bring new unity among the ninja villages as everyone comes together to protect the new life. And the story could explore how female Naruto passes on her ninja values to her child from a very young age.
One possible plot could be that Rachel gives birth during a big performance. Maybe she has been hiding her pregnancy from most of the glee club members, and right in the middle of a huge show, her water breaks. This leads to a chaotic but heartwarming situation where her friends rally around her, turning the backstage area into an impromptu delivery room while still trying to keep the show going in some way outside.