All of the NetNavis in DenTech City are turning into cats! A freak electrical storm released a Cat Virus that's causing the transformations. To add to the confusion, Rush has somehow materialized in the human world. Dr. Hikari shows up to lend his help, and he reveals that if the Cat Virus isn't stopped soon, MegaMan and the others will remain cats forever! After sixty-foot-tall versions of Rush and the Cat Virus face off in the human world, MegaMan and the others are able to defeat the Cat Virus and give Dr. Hikari the data he needs to write a vaccine program. Everything goes back to normal--except that Rush can still appear in the human world. Will the vaccine work? And why is Rush now suddenly able to appear in the human world whenever he wants? What is going on?