okay i'll try to explain.
genis shows up on asgard to find out what makes one a god.. thor gets mad after a while due to genis being crazy and insulting.. he attacks him.
the brother's shows up to reclaim what was there's that Odin stole eons ago and lied to his ppl about. Thor now in charge calls genis a liar a fight begins but it all happen in king thor's mind...
reality shifts back and thor realizes it was an illusion but not really since it was cosmic awareness sharing genis tries to settle it but the giant brothers or at least one of them doesnt want too..
so genis shoots him dead. had the fight happen asgard or a large portion of it would have bn destroyed due to their power lvls.