Two Heroes in One

(Spoilers to those who haven't watched "Deku vs Kacchan part 2")

Izuku and Katsuki are stuck with their house arrest and are currently in the middle of their first. Of course, everyone had left to the mall, or went to visit their parents, or chose another option. But while Izuku and Katsuki are stuck cleaning, a surprise comes in the form of a villain, that had used their quirk of "Fusion", allowing the user to fuse any two objects, even human beings. The villain had somehow surpassed the security and had fused Izuku and Katsuki, before going to the school and launch an attack that was stopped by All Might, who had ran into the villain just outside the UA building. This is where the story starts.

(I don't have some top-notch grammar so please do correct me)
(Finally, Cover credit goes to https://www.deviantart.com/roneronturon/art/Izuku-x-Katsuki-606560678
so check them out)