Speaking of parallel timelines, we have to talk about the parallel timelines in the Dragon Ball world.
Okay, now let's sort out the concept of parallel timelines in the Dragon Ball world. (The following is entirely the author's personal opinion.)
First, why do parallel timelines come into being?
They arise when factors from outside a timeline interfere, changing the course it was originally supposed to take. That creates a parallel timeline. Only traveling counterclockwise creates a new parallel timeline; traveling clockwise has no effect. The Supreme Kai can use the power of the Time Ring to travel clockwise into the future, but traveling counterclockwise is strictly forbidden. This shows that traveling clockwise does not create a parallel timeline.
In Dragon Ball Super, when the Supreme Kai of Universe 10 brought out the Time Rings during the Zamasu Saga, there were six rings in the box, which meant there were six parallel timelines in total. From his conversation with Zamasu, we learned that a highly advanced civilization capable of building a Time Machine had once arisen in Universe 12, creating a parallel timeline (Timeline B, with the original timeline being Timeline A).
Because the divergence between these two timelines happened in Universe 12, the development of Universe 7 was unaffected, and events unfolded identically in both.
Future Trunks from Timeline A couldn't find Dr. Gero's laboratory, or else found only its ruins without discovering the lab hidden underground. As a result, Cell from Timeline A developed safely.
For this reason, Future Trunks from Timeline A took the Time Machine back to the past (creating Timeline C) and brought medicine for the heart disease. Before Android 17 and Android 18 could be activated, he found the laboratory and the blueprints for the two Androids, successfully built a remote control, and destroyed the Androids. Since there was no Cell in Timeline C, Future Trunks didn't pay much attention to the embryo in the underground lab. It was probably no stronger than Android 17 or Android 18. After defeating the Androids, he had no reason to train with Vegeta, so his strength remained far too low.
After Future Trunks from Timeline A returned, he used the remote control to defeat the Androids. He may also have gone looking for the embryo in the underground lab, but Android 17 and Android 18 had destroyed the upper levels of the lab, which likely damaged the lower levels as well. When Cell was born, he also wrecked the underground lab, leaving it almost unrecognizable. This gave Trunks the mistaken impression that the embryo might have been killed in Android 17 and Android 18's attack, so he let his guard down. In the end, Cell from Timeline A ambushed him and took the Time Machine back to the past (creating Timeline D).
Things in Timeline B unfolded just like they had in Timeline A at first. But when it came time to travel back to the past in the Time Machine, things changed, quietly and without warning. Future Trunks from Timeline B traveled to Timeline D (creating Timeline E). After that, Timeline D unfolded just like the story, so Timeline D was the timeline shown in the series.
Future Trunks from Timeline B returned to Timeline B, defeated the Androids, destroyed Cell, and defeated Babidi and Dabura. Then Goku Black appeared, and in the end, Grand Zeno erased him.
With help from Future Trunks from Timeline A and no Cell, Timeline C made it safely through the Android Saga. It would most likely make it safely through the Majin Buu Saga as well. Goku from Timeline C had the heart medicine and didn't die, so after seven years of training, he would probably reach Super Saiyan 3. At the very least, he would reach Super Saiyan 2. Taking care of Dabura would be a breeze. Since Goku didn't die, Vegeta wouldn't keep pestering him to fight, so Majin Buu would never be revived.
Timeline D, the main timeline, reached the Dragon Ball Super era. The candidate Supreme Kai of Universe 10 learned from Shin, the Supreme Kai of Universe 7, that there was a human named Son Goku who was even more powerful than the gods. This filled him with resentment and gave rise to evil thoughts, until Beerus eventually destroyed him (creating Timeline F. This happened because Future Trunks from Timeline B couldn't defeat Goku Black and came to Timeline D for help. Influenced by the image of Future Trunks from Timeline B, Beerus destroyed Zamasu. Beerus was affected by factors from another timeline, which created a new one.)
In Timeline E, Future Trunks never traveled through time. Goku died of heart disease, the Androids ran rampant, and Cell developed in secret until he reached his perfect form. Whether Babidi would control him afterward or Majin Buu would kill him is anyone's guess.
Timeline F unfolded much like Timeline D, but Future Trunks never came to ask for help. Zamasu successfully stole Goku's body and went to Timeline B, where he and Zamasu from Timeline B wreaked havoc on Earth. Since Zamasu had destroyed the Super Dragon Balls, Goku here could only keep getting stronger while trapped in Zamasu's body.
In Timeline G, Future Trunks from Timeline B used the Time Machine to travel to a point before Babidi and Dabura appeared, since Timeline B had been erased by Grand Zeno. With Future Trunks from Timeline B and Future Trunks from Timeline G both there to protect them, the people would most likely be able to live in peace.
That covers all the parallel timelines that appeared in the Dragon Ball story.
There were seven timelines in total. One was erased by Grand Zeno, leaving six, corresponding to the six Time Rings.
All six timelines were under Grand Zeno's rule, with complete divine hierarchies, and were called the Omni-Universe.
All those fan-made comics and GT can be classified as fragments of timelines, incomplete universes.
Okay, that's all for parallel timelines. Let's get back to the story.
Future Trunks settled down here.
The number of people Gogito trained went from one to two. It made no difference. Herding one sheep or two sheep was all the same.
Future Trunks was still a good deal stronger than Trunks. Future Trunks was at least at the Super Saiyan 3 level, while Trunks hadn't even reached Super Saiyan 2. They were both Trunks, so why was the gap between them so huge? Gogito sighed inwardly.
Future Trunks had already perfected his transformation. His Super Saiyan 2 form had the power of Super Saiyan 3, and he'd reached his limit. To get stronger, he could only try Super Saiyan 3 or God Ki. As luck would have it, Gogito was learning about those, too, so the two of them studied together.
Future Trunks had spent some time in the other timeline and trained with Vegeta, so he was very familiar with God Ki.
Future Trunks: "When your dad beats you up every day, how could you not be familiar with it?"
Some time passed.
Half a month later, Gogito had mastered God Ki and learned to transform into a Super Saiyan God. He still couldn't go Super Saiyan Blue; he needed to become more familiar with God Ki and learn to control it better.
Future Trunks had also made some progress. He was confident he'd be able to transform before long.
As for Trunks, he had only just reached the second grade of Super Saiyan. He'd barely learned to transform before Future Trunks gave him a thorough thrashing. Future Trunks could just about use God Ki freely and needed someone to test it on, so Trunks got the worst of it and became his punching bag.
Seeing how powerful his other self was, Trunks gave it everything he had and trained like his life depended on it. He was starting to take after Vegeta.
Let's turn back time to a little over half a month ago, on Earth.
Before you continue