Yes, there might be. There are many fanfic communities out there where such stories could exist. You could try searching on popular fanfic websites like Archive of Our Own or FanFiction.net.
I don't have the definite answer to who Jiro ends up with. The manga could have many twists and turns before revealing the final pairing. It's all part of the excitement of following the story!
In the manga, Jiro and Akari do end up together. The plot builds up their connection gradually, with various challenges and moments that strengthen their bond.
Well, Jiro Horikoshi's wife was an important part of his life. Naoko Satomi supported him to some extent. Their story reflects the personal side of Jiro's life, which was intertwined with his great engineering feats. He was so dedicated to his work, and his wife was there in his life during those times, facing the challenges that came with the era, like the pre - war and war - time situations in Japan.
One possible fanfiction could be about Mimiko and Jiro going on a secret adventure together. Maybe they discover a hidden part of their world that no one else knows about. They could face challenges there and their relationship could grow stronger as they rely on each other to get through it.
Well, it could be about Jiro falling in love with Mimiko who is a vampire. Maybe Jiro discovers Mimiko's secret and has to decide whether to accept her or not.
Several characters have met their demise in the MHA manga, but it's a bit complex to list them all precisely. Some of the notable ones include [mention specific characters if known].