Mike didn't know it at first- he thought he just had the flu. But after arriving back in Hawkins after the events of Stranger Things 4 and he learns of the symptoms of Vecna's curse he doesn't think it's a big deal- Vecna had already chosen all his victims to open the gate. But Vecna still has the connection to Mike. Vecna decided to abuse this connection. AKA Mike possessed/mind controlled by Vecna Heavily inspired by a one-shot I read on Ao3 -Has both Byler and Mileven -Taken place a little over a month after the last shot of season 4