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.
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 popular theme is their friendship. Despite their differences, they are both dedicated teachers at Hogwarts, and fanfictions often explore how they might support each other behind the scenes. Another theme is their possible romantic relationships, not necessarily with each other, but how their views on love and relationships might be. For example, Snape's unrequited love for Lily could be contrasted with McGonagall's more reserved approach to love. Also, their roles during the wizarding wars are often explored in fanfictions. How they coped with the danger, made decisions, and protected the students.
For Minerva, you could explore her more emotional side. In fanfiction, show her struggling with her feelings for Severus. Maybe she has always seen him as a difficult colleague, but then realizes there is more to him. For Severus, delve deeper into his loyalty. You can write about how his loyalty to Dumbledore and Hogwarts extends to his relationship with Minerva. For example, he would do anything to protect her when Hogwarts is in danger because she is an important part of what he is protecting.
Their different personalities make it interesting. Snape is brooding and often seen as a bit of an outsider, while McGonagall is strict but fair. The contrast between them gives a lot of room for creative writing. For example, how they handle discipline in their respective houses is very different, and fanfictions can explore the clashes or agreements that might occur.
One interesting plotline could be McGonagall mentoring a young and troubled student. It would show her nurturing side, which we don't always see in the original books. Another could be her taking on a special mission during the war, like protecting a secret magical artifact. This would highlight her bravery and loyalty to the wizarding world.
Another plotline might involve a time - travel scenario where Harry Potter and Minerva McGonagall have to work together to change an event in the past that is threatening the future of the wizarding world. This could lead to some really cool interactions as they navigate through different eras.
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.
How about a story where Hermione discovers a hidden talent for transfiguration that even McGonagall is surprised by. They then work together to perfect this new form of transfiguration, but face opposition from some of the more traditional - minded professors. Or, in a post - war Hogwarts, they collaborate to reform the curriculum to include more practical and modern magic, all while dealing with the after - effects of the war on the students and the school.
In some fanfictions, Minerva adopts Harry after realizing the Dursleys are mistreating him. She then takes on the role of a mother figure, which is a huge change for Harry. This could include her taking him shopping for new robes and school supplies in a more loving and nurturing way than the Dursleys ever did. She might also introduce him to the wizarding world in a more personal and gentle way, making him feel truly welcome.