The Marvel Cinematic Universe isn't the first franchise to dabble in time travel and multiverse theory. Dragon Ball, perhaps the most globally renowned name in anime and manga, incorporated both time travel and the idea of multiple universes during the Dragon Ball Z and Dragon Ball Super narratives. Both series are regarded as successful, and have contributed their own respective wealths of rich narratives and remarkable characters.
One character who appears in both series is the time-traveling swordsman known as Future Trunks. The child of principal character Bulma and the mighty Saiyan prince Vegeta, Future Trunks made his first appearance in DBZ when he traveled from the future and easily cut down a mechanized Frieza and his hulking father King Cold. While a gifted, supremely powerful fighter in his own right, Trunks is also one of the few members of the Dragon Team to use a weapon, in this case a longsword. However, the origins behind the sword and how Future Trunks came to wield it are unclear.
Although treated as non-canonical, a young Trunks is presented with a weapon known as the Brave Sword -- an enchanted sword that bears an uncanny resemblance to the one Future Trunks wields in DBZ and DBS -- in the feature length film Dragon Ball Z: Wrath of the Dragon. Tapion, the Brave Sword's initial wielder, gives it to Trunks at the film's conclusion. He even goes so far as to imply the weapon was always meant to belong to him, potentially referencing Trunks' super-strong future self. While this appears to be the weapon's most straightforward origin, it seems unlikely that Future Trunks' sword is the same one that Tapion bestows on him.
Future Trunks and his younger, green-clad counterpart occupy different timelines. In Future Trunks' time, Dr. Gero's androids awaken unimpeded, defeat the Z Fighters -- including Piccolo, consequently nullifying the dragon balls -- and proceed to terrorize the planet. As the events of Wrath of the Dragon rely upon the use of the dragon balls, they couldn't have taken place in Future Trunks' timeline. Thus, it seems more likely that the conclusion of Wrath of the Dragon is meant to tie into the (also non-canonical) Dragon Ball GT series, as Trunks is depicted using a sword in the opening credits.
Outside of Wrath of the Dragon, viewers aren't shown a moment where Future Trunks explicitly receives either the sword he wields in Dragon Ball Z's "Android" saga or Dragon Ball Super's "Future Trunks" saga. However, based on Future Trunks' history, there's one possibility as to how he came to possess his sword: his teacher and friend, the late Future Gohan.
As depicted in the special Dragon Ball Z: The History of Trunks, Gohan managed to escape the tyranny of Androids 17 and 18 and live to adulthood. He then took it upon himself to train Trunks to access his full power and master the Super Saiyan transformation. Later in the special, after Future Gohan's death, Trunks is seen using his trademark sword.
Given the timeliness of the sword's appearance, it seems logical that Gohan gave the sword to Trunks at some point during their training. After all, Gohan himself received a sword from Piccolo while under his brutal tutelage, so it would make sense for Gohan to grant a similar gift to his own protege.
Acclaimed as it is, Future Trunks' sword isn't infallible. In a battle with Android 18, the sword is broken beyond repair, forcing Trunks to sheath it for the remainder of his time in DBZ. When he later appears in DBS, Future Trunks sports another sword, but it too is broken by Fused Zamasu. However, Trunks has the power to infuse the broken blade with ki, creating the Sword of Hope and ultimately defeating the deadly villain.
The details behind Future Trunks' weapon are convoluted, even frustrating. That said, the sword's ambiguous origins may be intentional. After all, as Future Trunks says in his altercation with King Cold, "It's not the weapon that makes the man."
