I'm not sure specifically as I haven't read it in detail. But generally, it might be about some kind of relationship, perhaps a romantic one, and the 'kiseki' could imply some sort of miracle or special event in the story.
Well, in this 'kuro meets emiya fanfiction', it could be about a crossover of their respective storylines. For example, if Kuro is from one series and Emiya from another, the fanfiction could blend the elements of both worlds. It could be full of action as they fight together against a common enemy, or it could be a more character - driven story exploring their relationship.
Kuro remains alive throughout the Haikyuu manga. The plot doesn't take such a tragic turn for this character. Instead, it emphasizes the team's journey and their passion for volleyball.
I don't know the main characters in 'kiseki dear to me novel' as I haven't read it. But usually, the main characters are the ones who drive the story forward, so they could be characters with strong personalities or those with important goals in the context of the story.
One possible plot could be that Kuro and Emiya meet in a mysterious realm. They are initially suspicious of each other but then realize they share a common goal, like saving the realm from a dark force. So, they team up and use their unique abilities to fight the evil.
The uniqueness of 'naruto kuro tenshi fanfiction' lies in the combination of the Naruto universe with the concept of a 'kuro tenshi' or black angel. It brings in a new and often dark or mysterious element that isn't part of the original Naruto.