While the Dragon Ball franchise has always been about increasingly more powerful combat transformations, the anime series Dragon Ball Super took things even further beyond by introducing the concept of its Saiyan characters gaining the battle strength of the gods themselves. This resulted in Goku and Vegeta achieving a new transformation known as Super Saiyan God, making them far more powerful than Super Saiyan 3 and able to stand toe-to-toe against Beerus, the God of Destruction. While this transformation would elude most of the series' cast, the non-canonical arcade game Super Dragon Ball Heroes and its subsequent anime adaptation saw the fan-favorite character Trunks achieve the transformation for himself in content currently only available in Japan.
Dragon Ball Heroes introduces Xeno, or Time Patrol Trunks, a time-traveling version of the hardened, adult version of Vegeta and Bulma's Super Saiyan son. This alternate version of Trunks mirrored much of his counterpart's history in the main timeline, including traveling back in time to help save Goku's life and defeat the Androids and Cell before returning to his own divergent future. Xeno Trunks was confronted by the Time Patrol for breaking the laws of the space-time continuum and recruited among their number by the Supreme Kai of Time to help stop the villainous Mira from causing disastrous disruptions to the timeline; guiding the player characters with other classic Z Fighters across the franchise's expansive history.
Xeno Trunks leads the Time Patrol to the Dragon Ball GT timeline at the climactic moment when Super Saiyan 4 Gogeta is battling Omega Shenron at the end of the anime series. There, the assembled heroes learn about the Demon Gods, led by their king Mechikabura, who escaped from his time prison to threaten the entire space-time continuum. As the battle against the demons intensifies, Xeno Trunks transforms into Super Saiyan 3 while Xeno Gohan transforms into Super Saiyan 4. Despite this, the Time Patrol is unable to defeat Mechikabura who easily defeats them all. With desperation mounting, the battered Saiyans lend their power to Trunks to cause him to transform into a Super Saiyan God for the first time.
Dragon Ball Super begins with the discovery of a ritual that allowed a Saiyan to make the divine combat transformation if five other Saiyans channeled their energy into the recipient. Goku was the first character to make this transformation following Beerus' arrival on Earth while Vegeta similarly unlocks the form after undergoing rigorous training under Beerus's angelic attendant Whis. The transformation makes its users visibly calmer while consuming considerably less energy than the later Super Saiyan God or Ultra Instinct transformations.
In his new transformation, Super Saiyan God Trunks is able to reclaim and recharge his signature Key Sword and use it to defeat Mechikabura, sealing the demon king away in the Eternal Labyrinth and preserving the space-time continuum once again. In the ninth anniversary book for the arcade game, the developers revealed that they had originally intended for Xeno Trunks to transform into Super Saiyan 4, like Xeno Gohan, instead of Super Saiyan God. However, a debate arose as to whether Trunks' hair should revert to purple or change to black like Goku and Vegeta in the form. Unable to reach a consensus, the developers opted to have Xeno Trunks transform into Super Saiyan God instead, sidestepping the debate altogether.
While Super Dragon Ball Heroes and its subsequent adaptations in manga and anime are not considered part of the main canon, Trunks' transformation marks the first time a Saiyan-human hybrid is seen achieving the form in any form of media from the franchise. And with the canonical franchise still determining its next steps after the successful release of Dragon Ball Super: Broly, perhaps some of the arcade game's concepts could find themselves incorporated into the main mythos moving forward.