One possible plot could be that Jasper and Bella face many challenges in raising their baby in a world full of supernatural elements. Their baby might inherit unique powers from both of them, and they have to protect the baby from those who might want to use its powers for their own gain.
In this fanfiction, the baby could be a key to solving some long - standing mysteries in their world. For example, the baby's very existence could start to change the power dynamics among vampires, werewolves, and other creatures. Jasper and Bella would then have to navigate these changes while also dealing with the normal parenting tasks like teaching the baby right from wrong, and ensuring its safety. They might also have to deal with the reactions of their friends and families, some of whom might be overjoyed while others could be jealous or fearful of the baby's potential.
Perhaps the fanfiction could focus on how Jasper and Bella's relationship evolves with the addition of a baby. They might struggle at first to adjust to their new roles as parents. Bella could be overprotective while Jasper uses his calm nature to soothe both Bella and the baby. And the baby could be a symbol of hope for a more peaceful co - existence between different supernatural groups.