I'm not sure specifically as it could be about various things. It might be a fan - created story involving characters named Hopper and Flik. Maybe it's a story that explores their relationship, perhaps a friendship or an adventure they go on together.
Start with the official fan communities related to the source material of Hopper and Flik. There might be dedicated sections or threads where fans share their fanfics. Additionally, search engines can be useful. Just type in 'hopper x flik fanfic' and see what comes up. But be cautious of clicking on untrusted websites.
Another idea is a fanfic set in an alternate universe where Flik and Hopper are not enemies. They could be friends from the start and go on adventures together. For example, they might discover a new land filled with strange and wonderful insects, and their friendship is tested as they face various challenges during their exploration.
You can start by brainstorming different scenarios. What if Hopper got injured and Flik had to help him? Or what if Flik was captured by Hopper's gang and had to find a way to escape? Once you have a scenario in mind, start writing the first few paragraphs. Describe the scene, the emotions of the characters. Maybe start with Flik's point of view as he sees Hopper approaching, his heart pounding with a mix of fear and determination.
Another theme is family. They both have a connection to the kids in Hawkins, and often in these fanfics, their relationship becomes a way to create a stronger family unit. They support each other in parenting the kids, which is really endearing.
One great 'hopper x joyce fanfic' is 'A New Beginning'. It focuses on how Hopper and Joyce start to build a relationship after all the chaos in Hawkins. It beautifully portrays their shared experiences and how they support each other.