Well, some fanfictions about Mosquito Girl in OPM can be really creative. They often explore her backstory more deeply, like how she became the way she is. It gives fans a chance to see different sides of her character that might not be shown in the original work.
One common theme is her struggle for survival. Since she's a monster in the OPM world, she has to constantly deal with threats from heroes. Fanfictions often explore how she tries to stay alive in this hostile environment.
One interesting aspect could be the unique interpretations of the Mosquito Girl character. In some fanfics, her backstory might be explored more deeply, like how she became the way she is in the original One - Punch Man story. It could also show different relationships she might have with other characters in the OPM universe that were not fully explored in the official story.
You can start by looking on popular fanfiction websites such as Archive of Our Own (AO3). It has a large collection of One - Punch Man fanfics, and you can use the search function to specifically look for those related to Mosquito Girl. Another option is FanFiction.net, which also has a decent number of OPM fanfics.
Yes, the OPM manga has come to an end. The creators completed the narrative, providing closure to the fans. Although some might have hoped for more, what was presented was a comprehensive and conclusive tale.