After Buu was reborn, it ended with most of earth's warriors dying in the process to take down Buu, including Vegeta and Goku, leaving earth unprotected outside of you and Gohan, which was a golden opportunity when bulma detected two saiyans having landed on earth, paragus and Broly once again for a third time in an mountainous region of earth, it was ignored by everyone for a little while until west city was suddenly destroyed by a singular ki blast, killing thousands

Gohan: “This has to be broly's doing! We have to stop him before he kills anymore people!”

You and Gohan fly towards the destroyed west city, leaving Gotenks and trunks with bulma and chi chi even though they wanted to fight as well