Honestly, 'y f n' in fanfic could be a random combination of letters without a widely recognized meaning. Maybe it's a made-up term by the author for a special plot element or character trait.
Well, Mikey might be a bit surprised at first. He would probably be intrigued by the different scenarios the fanfiction presents about Takemichi. Draken, on the other hand, might be more critical and analyze how the fanfiction portrays Takemichi's growth and relationships. Mitsuya could find it interesting from an artistic point of view, seeing how the writer has used Takemichi's character to create new stories.