Yes, there are quite a few. You can try searching on fanfiction platforms like Archive of Our Own. Just type in the relevant keywords, and you'll likely find some interesting stories.
One common theme is the culture shock. Since Harry and Blaise come from different backgrounds, there can be a lot of misunderstandings and adjustments.
If an accidental potion causes Blaise to lose his voice, it would be a big challenge for him. He's used to being able to communicate his thoughts and opinions, especially in a place like Hogwarts where social status and being able to speak up matter. This would force him to find other ways to interact with his friends and classmates, like using magic to write messages in the air. And it could also lead to some misunderstandings, especially if others misinterpret his silence.
One interesting plot twist could be when a potion that was meant to be a simple healing draught accidentally turns into a truth - revealing potion. This might lead to characters revealing secrets they never intended to. Another could be a potion that causes temporary magical ability swaps among the characters, like Blaise and another student, which would create a lot of chaos and new interactions.
He might be suspicious at first. Given their different houses and the general tensions between Slytherin and Gryffindor, Harry would be cautious about Blaise's motives.
One popular 'Blaise and Harry boyfriends fanfic' is 'The Unlikely Bond'. It has a great plot where Blaise and Harry start off as rivals but gradually develop a deep emotional connection. The author does an amazing job of portraying their relationship growth, from hesitant friendship to a loving relationship.
Perhaps it's a warning. There might be some danger approaching Harry, and Blaise, having come across this information, decides to inform him. For example, if there's a new dark wizard in the school or some sort of plot against Harry that Blaise has uncovered.
A possible plotline is dealing with the media in the wizarding world. As Harry is a very well - known figure, their marriage would be big news. There could be tabloids writing all sorts of things about them, and they would have to handle the public scrutiny. Also, a plotline could involve them mentoring young wizards. Their unique relationship could be an example for the younger generation to learn about acceptance and different kinds of love. And they could pass on their magical skills in a new and innovative way.
Another theme might be the reaction of the wizarding world to such an unusual situation. It can be about how society views their relationship and the pregnancy, and how Blaise and Harry navigate through the potential prejudices and challenges. In many fanfics, this can lead to some interesting plot developments as they try to protect their family and each other.
There are some. However, the quality can vary greatly. Some might focus more on the relationship development between Harry and Blaise, while others could be more action - packed with their interactions being part of a larger plot. It really depends on what you're looking for in a fanfic.