A possible plot is that Severus discovers a new potion that can enhance the magical abilities of the unborn child. Minerva is hesitant at first, but Severus convinces her to let him try it on a small scale. Meanwhile, they have to navigate the challenges of Minerva still teaching her classes and Severus doing his potions work. They also face some opposition from certain members of the wizarding community who think their relationship is inappropriate. But they stand strong together and look forward to the arrival of their baby.
One possible plot could be the challenges they face in their relationship due to the unexpected pregnancy. Maybe they have to deal with the reactions of their friends and family. Another plot could involve how they prepare for the arrival of the baby, like Severus trying to be more responsible and Lily dealing with her own fears and hopes.
Severus, who was always a bit brooding and reserved, might become more protective. His focus would shift from just his potions and the dark arts to ensuring Minerva's and the baby's safety. He would be constantly on guard. Minerva, on the other hand, usually a strict and no - nonsense teacher, could become more emotional. Small things might make her cry or get overly excited. She might also be a bit more lenient with her students as she experiences the softer side of life through her pregnancy.
Another trope is the 'mentor - mentee' dynamic in reverse. Usually, they are both mentors to students, but in some fanfictions, they end up learning from each other. Snape might learn more about emotional openness from McGonagall, while she could learn about some of the darker arts and how to better protect students from Snape. It's an interesting flip of their usual roles.
One great Severus Snape and Minerva McGonagall fanfiction is 'The Unlikely Alliance'. In this story, they are forced to work together on a Hogwarts project. Their different teaching styles and personalities create interesting interactions. Snape's brooding nature contrasts with McGonagall's more no - nonsense approach, and as they overcome obstacles in the project, they also start to understand each other better on a personal level.
In some Albus and Minerva baby fanfiction, the plot could revolve around the baby being a key to uniting different magical communities. Albus and Minerva find themselves in the middle of this, having to raise the baby in a way that will make it able to fulfill this great destiny. They might face challenges like teaching the baby different magics from different cultures and dealing with jealousies or rivalries from other wizards who don't want this unity to happen.
One idea could be a story where Minerva and Severus have to team up to protect Hogwarts during a new, unexpected threat. Maybe a dark magic artifact is discovered near the school and they must use their combined knowledge and skills to keep it from falling into the wrong hands.
One interesting plot could be Minerva mentoring a young witch or wizard who has unique magical abilities. She could help the student discover and control their powers, much like she does with her students at Hogwarts. For example, the student might have an affinity for an ancient and forgotten branch of magic, and Minerva uses her vast knowledge to guide them.
One interesting plot could be how Hermione adjusts to her new family life with Minerva and Albus. Maybe she starts to learn different magical skills from them in a more personalized way compared to at Hogwarts.
One interesting plot could be Severus having to deal with Harry's fame at Hogwarts while trying to keep their new family relationship a secret. It adds a layer of mystery and tension.
Well, one interesting plot could be Harry seeing Severus in a new light. He realizes that Severus was actually a complex and misunderstood character. So, he decides to adopt him to give him a new start in life. Another plot might involve Severus initially being resistant to the idea of being adopted by Harry, but over time, he warms up to the concept as he sees Harry's genuine kindness.