If you are trying to open this file, you will need a utility like 7-Zip or WinZip to extract its contents and see the "story" inside.
Wikipedia notes that 7-Zip is an open-source tool used for high-ratio file compression. MAIS.7z
The search results indicate that likely refers to a compressed archive file (with the .7z extension) named "MAIS." However, there is no widely known viral story, game, or cultural phenomenon specifically titled "MAIS.7z" in general public databases. If you are trying to open this file,
A 7-Zip file containing a visual novel, a game's story assets, or a collection of digital stories. a game's story assets