Short Summery

Future Trunks returns and his home is once again being destroyed by a powerful foe, but this one looks really familiar.

Tropes

Call-Back: The starry goo Bulma made in the beginning of the last arc turns out to be a fuel source needed to power a time machine.
Dystopia: Once again, Future Trunks’s timeline is a devastated wasteland.
Happy Ending Override: When we last saw Future Trunks, he had grown powerful enough to kill the androids and Cell single handily and it looked like the future was looking brighter. But now a new threat has arrived and apparently he isn't strong enough to fight it.
Heroic Sacrifice: Both Future Bulma and Future Mai op to try to hold off the mysterious attacker and buy Trunks time to get to the time machine.
Wham Shot: The end of the beginning of the arc has the assailant finally show himself and it's... Goku?