Darsh comes into the DB universe and starts mucking stuff up so naturally Goku and Vegeta don't like this. Because of his ridiculous power level they decide to fuse and become Vegito. Whis and Bills decide to help Vegito because Darsh scares the hell out of them too.
-Goku and Vegeta are current (The return of F)
-Anything written by Akira is useable for the DB characters
-Darsh is stuck in base form
Fight takes place in some empty solar system.