On a seemingly normal day in Lakewood Plaza Turbo, K.O. finds a strange letter which is an invitation for him to come to a fighting tournament called Super Smash Bros. However, as soon as he arrives at the Smash Mansion, things get absolutely crazy, including an ensemble formed by Master Hand and several other villains who want to get him out of the tournament since "cartoon characters don't belong in Smash". K.O. of course, wants to prove the ensemble otherwise and forms a rag-tag team with his friends from Lakewood Plaza and a few Assist Trophies who also wish to be Smashers called the Let's Be Smashers. However, as the hype for Smash Ultimate goes on, the LBS soon find themselves facing off against much bigger threats.