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.
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.
Maybe the love letter contains his deep admiration for Ginny's bravery. He could mention how she always stands up for what she believes in, whether it's against the Dark Arts or for the rights of house - elves. He might also share some of his insecurities and how Ginny makes him feel more confident, like when she supported him during his difficult times fighting Voldemort.
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.
In this kind of fanfic, it might start with Harry having access to a troll. He could have found it in the Forbidden Forest or some other mysterious place. He then decides to send it to school for various reasons. It could be to teach a bully a lesson. Once the troll arrives at school, there would be pandemonium. Students would be running and screaming. Teachers would be trying to protect the students and subdue the troll. Harry would then be in a moral dilemma, realizing the seriousness of what he has done and trying to fix the situation before anyone gets seriously hurt.
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.
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.
A unique aspect can be the way they rewrite the Hogwarts social dynamics. Usually, Gryffindor and Slytherin are seen as rivals, but in these fanfics, Blaise and Harry's relationship bridges that gap. It gives a fresh perspective on the wizarding world's relationships and hierarchies. For example, in some fanfics, they team up to change some of the old - fashioned rules at Hogwarts.