Most likely not. While the Harry Potter series has inspired a vast amount of fanfiction, concepts that involve a rather odd or unconnected element like 'Kira' are not likely to gain mainstream popularity. Fans are generally more drawn to fanfictions that expand on the existing Harry Potter lore, such as delving deeper into the backstories of minor characters or exploring new magical concepts within the established universe. This 'harry potter is kira fanfiction' seems like a very specific and rather random combination that would only appeal to a very small subset of fans who are interested in very off - the - wall crossovers.
I don't think it's a widely popular concept. Harry Potter has its own huge fan base and a lot of traditional fanfiction focuses on the original characters and storylines within the Potterverse. The idea of mixing it with something named 'Kira' which is not a common part of the Harry Potter world is likely to be a niche concept.
No, it's probably not a popular concept. The Harry Potter fandom is massive and there are many well - known types of fanfiction, like those exploring different relationships between the main characters, or what - if scenarios within the original story. The 'Kira' element is quite out of place in the Harry Potter world. It's not something that most Harry Potter fans would immediately be interested in, unless there is a very specific and well - executed take on it. Since it's not based on any official crossover or a widely known combination, it's likely to be a relatively unknown and unpopular concept.