Thirteen years had passed since the androids had turned life on earth to hell, taking away from Gohan nearly everyone he ever cared for. Since then Gohan had tried many times, to no avail, to beat the androids but each time he was defeated. Each time the androids let him know he only lived for their amusement.
Gohan was currently on his way to visit trunks when an explosion rang out from a nearby city, as Gohan made his way there he saw trunks lying on the floor with the android number 17's foot on him. Gohan landed down and let his anger flood him to trigger the change into a super saiyan.
"Remove your foot from him 17!" Gohan shouted.
"Make me." Android 17 said with a challenging smile.
Gohan charged at android 17 delivering a few punches all of which 17 blocked with one hand before punching Gohan and sending him flying backwards. Android 17 then flew after Gohan delivering a few more hits before delivering a blast which completely engulfed Gohan.
"No!" Trunks shouted.
"Don't worry weakling," Android 17 taunted, "that blast wasn't enough to kill him."
"Your still as weak as ever, young Gohan" Android 18 said, "but at least you've grown into a handsome man."
"See you around Gohan, hopefully next time you'll be more fun to battle." Android 17 mocked.
After flying up about 30 feet, android 17 stopped suddenly, and sent a flurry of blasts into the city destroying the ruins even more. Gohan was barely able to get up and get trunks to safety before he felt a searing pain in his arm, before he could look to see what happened he passed out from the pain.
Gohan woke in what seemed like days later with a profound feeling of loss. He tried to sit up but was pushed back down by Bulma. Over the years she had not changed much, her hair was still in a different hairstyle every month and her face hadn't changed much except for a few lines here and there.
"Rest some more Gohan" Bulma urged.
Gohan just looked at her before he realized just why he had a feeling of loss; he looked down and saw that his left arm was no longer attached to his body!
"W-what the…" Gohan started but he just couldn't finish without letting the side of him he never let out free.
"You lost your arm protecting me" Trunks said from the corner of the room he sat in.
"It's not your fault Trunks" Gohan said
It had always baffled him, how he always felt the strong urge to protect and even comfort Trunks ever since the first time he had met the boy.
"Yes it is," Trunks muttered, "if I had been as strong as you, you wouldn't have had to protect me and I could have helped you instead of making you weaker."
"Trunks," Gohan began, "Even if you were a super saiyan you couldn't have done anything"
"Gohan" Bulma shouted, "don't say that!"
"No bulma he needs to hear it," Gohan said in a calm voice, "Even as a super saiyan I haven't even been able to scratch them. Maybe they're unbeatable, I don't know but I do know even if you became a super saiyan it would take a lot more than just transforming to beat them."
"THEN WHAT SHOULD I DO?!" Trunks shouted furiously at the man whom he looked up to, the man he thought was stronger than anyone else.
"Train with me," Gohan said, "I need to train as well, to re-learn how to fight without my left arm."
Gohan put his hand on his left shoulder taking a moment of silence for his fallen limb. He inwardly prayed trunks would accept his offer as the boy remained silent with his head down for what seemed like hours.
"Alright," Trunks responded after a few minutes, "I'll train with you"
"Good." Gohan replied with a smile.
Over the next week Gohan and Trunks trained together in the mountains, trunks learning to hone his senses and Gohan learning to block and cover his left side. All the while both knew deep down the androids were killing people, but they also knew they weren't strong enough to defeat the androids as they were. So they continued to train with each other, honing both their senses and skills with the hopes of becoming strong enough to defeat the androids.
From here on the story will take a different path then the manga/anime.