It could also be an invitation. Blaise might be inviting Harry to join a secret club or a special event. Maybe it's a club for students who are interested in a particular type of magic that isn't taught in regular classes, and Blaise thinks Harry would be a great addition.
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.
Maybe she's sharing some secrets about the wizarding world that she has come across. It could be something related to a hidden magical artifact or an old family spell.
One possible outcome could be that Harry realizes he doesn't want either of them and decides to focus on his own life and friendships. He might see their fight as childish and a distraction from more important things like his studies or fighting against the dark forces in the wizarding world.
Well, perhaps it could start with some sort of magical mix - up. Maybe a spell gone wrong during a celebration. Harry and Blaise could find themselves suddenly married. Then they'd have to deal with the shock from their friends and family. For example, Hermione might be very confused and Ron could be outright shocked.
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.
Well, it could be that Blaise stumbles upon an old diary or artifact that belonged to Harry's mother. This discovery sets him on a path to understand more about her and, in turn, about Harry. It might lead to a series of events where Blaise has to protect this new - found knowledge from dark forces in the wizarding world who would use it for evil.
One possible scenario in this fanfic could be that Harry and Blaise are working on a difficult potion in Potions class. Maybe they accidentally add the wrong ingredient due to a misunderstanding or a distraction. This could lead to a potion that has unexpected effects, like making them swap voices or even temporarily change their physical appearances.
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.
Maybe in a social setting where there are rumors or false accusations against Harry. Blaise takes it upon himself to investigate and clear Harry's name, showing his protectiveness in a more subtle but important way.