Prologue
The destructive force of the Android 17 and Android 18's ki barrage attack was something never seen before. It left a swath of destruction in its wake, and the group had little idea what had happened to Future Gohan. Before they had time to even process what had happened, Future Gohan suddenly appeared alive, but injured and weary.
Trunks was the one who found him buried deep beneath the mud and debris, and his heart sank when he caught a glimpse of the person he had been searching relentlessly for. Future Gohan was in desperate need of help - he hadn't yet gotten over the drastic injuries sustained from the attack, and Trunks knew he had to act fast. He wasted no time and scooped him up, and started to make his way to Bulma's lab.
"Trunks! You made it!" Bulma exclaimed in relief when the young saiyan appeared. Without a moment to spare, she and Trunks were immediately tending to Future Gohan, getting him settled into a life support system to try to keep his condition steady until she could properly treat him.
"I know you want to go after the androids, Trunks," she said to the young warrior, "but that's not an option right now. They're too powerful for you to take on alone - you have to train and build your strength up first in order to even stand a chance against them."
Trunks grit his teeth in frustration, wanting badly to take revenge for the pain and suffering he had seen Future Gohan go through, but he knew Bulma was right. In order to protect those he cared about, and ensure the androids never hurt anyone ever again, he needed to build up his strength.
As Trunks left to begin training, Bulma worked tirelessly at her lab, using her vast scientific knowledge to work on the time machine and also prepare a robotic limb for Future Gohan. She salvaged parts from all over West City, and worked with an impressive level of detail and precision as she put it all together.