Dragon Ball Super brought back Future Trunks, one of the franchise's most popular characters. Introduced in Dragon Ball Z before the Androids appeared, this version of Trunks was a much less lively character compared to his mainstream universe counterpart. He also had a solid but tragic friendship with Goku's son Gohan.
Trunks' Future incarnation would go on to live a life that, in many ways, mirrored the life of the mainstream universe's Gohan, though it still unfolded in a much more tragic way. Here's how the purple-haired Saiyan reflected the life of his mentor, or at least, a version of him.
How Future Trunks' Life Mirrors Gohan
One of the biggest ways Future Trunks and his mentor mirrored each other was how they gained access to the Super Saiyan 2 transformation. In both cases, it involved the death or beating of someone else, sending the young half-Saiyans over the edge. In Gohan's case, it's seeing the noble Android 16 being mercilessly killed by Cell that finally unleashes his power, but for Trunks, it was seeing Shin being attacked by Babidi that triggered Super Saiayan 2. Notable battles of theirs included fights against Cell and Dabura, who they were both able to defeat in their respective timelines.
They were also both able to successfully pull out and wield the Z Sword, in spite of them both being "mere mortals" for whom such a task should be impossible. They also later broke these swords, in one timeline this breaking resulting in a positive outcome and the other a much more tragic one. In the case of Gohan, he broke the Z Sword when he tried to strike a cube of Katchin, an extremely powerful and dense material.
Future Trunks, on the other hand, broke the sword when Dabura spat on it, quickly petrifying it. Letting it go so as to not become stone himself, Trunks' release of the sword caused it to shatter as it hit the ground. In the mainstream universe, the sword's destruction released the Old Kai, when in Future Trunks' world, it meant that he was gone for good. This sadly reflects the general tone of Future Trunks' world, which is far bleaker than the mainstream universe.
How Future Trunks' Life Differs from Gohan's
The world that Future Trunks lives in is one without the old team of Z Fighters, leaving much of Earth's defense to Trunks himself. This hones him into an incredibly powerful warrior, but also one who's seen and been through a lot for his age. Things only get worse, with threats such as the Androids, Cell and Babidi quickly escalating into even greater dangers like that of Goku Black.
The mainstream universe Gohan, on the other hand, lives a comparatively peaceful life both in Dragon Ball Super and the now non-canon Dragon Ball GT. He gives up fighting to become a studious and industrious civilian, living the type of life that many in Trunks' Universe 7 can only dream of. It's only after Future Trunks realizes this that he's able to lighten up around Gohan, feeling happy that he was able to find the peace that his own mentor never had. Sadly, their triumphs on the battlefield were some of the only areas where the two men had much in common, but hopefully one day with Future Mai, Trunks will be able to mirror Gohan in another way and find that same peace.