Dragon Ball Z Special 2 Zetsubou E No Hankou Nokosareta Chousenshi Gohan To Trunks Episode 1

It has been thirteen years since the Androids began their killing rampage and Son Gohan is the only person fighting back. He takes Bulma's son Trunks as a student and even gives his own life to save Trunks's. Now Trunks must figure out a way to change this apocalyptic future.