"Future" Trunks' Past is the 16th chapter of the Dragon Ball Super manga.
Future Trunks tells the story of the events that happened a few years ago. He is on the Sacred World of the Kai training with the Z-Sword, with Future Shin and Future Kibito watching him and praising his talent. Future Trunks thanks them, and says that on his own there is no way he could have gotten this strong. To finish his training, Future Shin summons a block of Katchin, the strongest metal in the universe, to test the cutting power of the Z-Sword. Before he can do this, however, Future Kibito senses that Future Babidi is on the move. The three head out to fight them, with Future Trunks asking if he can have his regular outfit back.
Late in the fight, Future Shin and Future Kibito are injured and tired while Future Trunks is fighting a losing battle with Future Dabura, with Future Babidi laughing. Future Dabura uses his Stone Spit, which Future Trunks blocks with the Z-Sword, and notices it is turning to stone. Future Shin quickly tells Future Trunks to drop the sword before the stone spreads to his body. Future Dabura quickly attacks Future Trunks with his sword, which Future Trunks manages to catch with his hands. The Z-Sword falls to the ground and shatters, much to Future Kibito's surprise. Future Dabura destroys the Z-Sword's remains and sends Future Trunks landing on the ground, claiming he will send the three of them to the afterlife. Future Shin apologizes to Future Trunks as he would not suspect Future Dabura to be a henchman. Future Babidi point out that Future Pui Pui and Future Yakon were only decoys to lure them there, and that it took him over 10 years to amass enough energy to resurrect Majin Buu. Future Shin, claiming that it will not happen, prepares to attack Future Babidi, but Future Dabura intercepts him, sending him crashing with a ki blast. Future Kibito prepares to save Future Shin, but Future Dabura suddenly appears in front of him and destroys him with a point-blank ki blast. Future Babidi proceeds to beat Future Shin, using his magic to torture him. Future Trunks, angry and at his breaking point, transforms into a Super Saiyan 2 and beats Future Dabura down, causing him to crash into Future Babidi. Future Dabura prepares his Evil Spear but he cannot throw it due to Future Shin freezing his movements with Telekinesis. Future Trunks takes this opportunity to fire a Burning Attack, destroying Future Dabura and Future Babidi. Future Shin, satisfied about their victory, collapses and succumbs to his injuries. Goku Black, watching over the fight, is overjoyed that he found a timeline where a God of Destruction is dead due to the Shin's death.
Future Trunks finishes his story by saying that after that, Goku Black proceeded to annihilate the humans. Beerus and Whis confirm their theory of the God of Destruction in the future being dead. Whis says that there are only a handful of individuals, being Gods and high-ranking individuals, that know about the God of Destruction and the Supreme Kai being linked, surmising that Goku Black must be on the level of Gods, also somehow having the ability to travel between parallel worlds. Beerus confirms with Future Trunks about there being no God of Destruction. Goku officially introduces Beerus and Whis to Future Trunks, who just now learned about the God of Destruction. Bulma dismisses the conversation and says their hands are tied until they accumulate enough energy for the Time Machine, and tells Future Trunks to change into some clean clothes. Future Trunks approaches Trunks and properly meets him, asking if he can already go Super Saiyan. Future Trunks is proud to hear that Trunks can, and tells him that protecting his family and friends are very important. Future Trunks also meets Mai, who is lovestruck by him, and tells her that she is still alive in the future, but tells Pilaf and Shu he never met them. After walking out, Future Trunks thinks about Future Mai. Trunks notices Mai's infatuation with Future Trunks and is disappointed.
In the alternate timeline, Goku Black tries searching for Future Trunks ki but realizes he completely disappeared. Black Goku says he already destroyed every Supreme Kai in each universe and wonders that with no Gods of Destruction and Future Trunks' disappearance, there is no one left to oppose him. He then says that this is far too boring. Goku Black flies away, saying there is something he has to check on. A grown-up Scratch is licking Future Mai's (presumably dead) body as the scene turns to the present, where everyone is eating in a restaurant. Dr. Briefs and Mrs. Briefs meet Future Trunks, incorrectly assuming he was Trunks who had undergone a growth spurt. Goku asks Future Trunks if he has any allies, and Future Trunks says he is the last warrior standing due to the deaths of the other Supreme Kais. Beerus wonders about a present Goku Black appearing and doing the same thing, and Whis suggests visiting Shin and asking him about anything suspicious.
The scene cuts to the Sacred World of the Kai of Universe 10, where Kibito is sparring with Zamasu and Gowasu is watching with Shin; Shin and Kibito paying a visit from Universe 7. Kibito is having a hard time fighting Zamasu, and before Zamasu can land a serious blow, Gowasu stops the fight. Zamasu thanks Kibito as Shin is utterly impressed by Zamasu's fighting prowess. Shin comments that even if they gathered every Shin, Zamasu would have no equal. Zamasu is impressed with the Universe 7 Kais, also praising their defeat of Majin Buu a few years back. Shin says that couldn't have done that with strength alone, as such duties fell under the God of Destruction's jurisduction, however Kibito says that even that posed a challenge for Beerus as he likes taking naps. Back on Earth, Beerus sneezes. Shin gives credit to Goku for his assistance, and Zamasu asks who he is. When Shin answers, Zamasu is surprised to learn a "mere mortal" gained power rivaling the Gods, and surmises that unnecessary existences should be eliminated. Shin (uncomfortably) agrees with him when he and Kibito leave to return to their own universe. Gowasu comments that while Zamasu's fighting prowess is second to none, he must learn to work on his inner self.
Gowasu orders Zamasu to observe Planet Babari and its inhabitants, watching them pummel each other. Gowasu asks Zamasu on his input on what they should do with the aggressive creatures, and Zamasu suggests they should be eliminated. Gowasu berates Zamasu for speaking so bluntly, telling him that such tasks are for the God of Destruction. Gowasu has been observing them for 1,000 years, seeing if they will discover harmony and peace, and when Zamasu is adamant on them remaining brutal and aggressive, Gowasu suggests using a Time Ring to travel through time and see if Zamasu was correct.
- Future Trunks (Super Saiyan/Super Saiyan 2), Future Shin, and Future Kibito vs. Future Babidi, Future Dabura, Future Pui Pui, and Future Yakon
- Kibito vs. Zamasu
Anime and Manga differences
- The past sequences showing Trunks and the Kaioshins battle with Babadi and Dabura is much more extensive than in the anime, showing that Trunks actually trained on the Sacred World of the Kais.
- In the manga Black does not travel back to the present to fight Goku.
- Future Trunks going to the restaurant with his friends and family does not happen in the anime.
- In the manga Zamasu fights against Kibito. In the anime they never met, instead Goku went with Beerus and Whis to their world and Goku fought him instead.