I've taken a couple liberties with the timeline (nothing major I think), having Bra be ~6 years younger than Trunks, and having the time span between the end of the Buu Saga and the end of the Baby Saga ~15 years.

For the sake of a more interesting story, I'm assuming Goten and Trunk can go SS2 and Vegeta can go SS3 as they have been training at least mildly intensively over the 15 years since the Buu Saga.

Goku was reverted back to an adult with the Dragon Balls.

The story will focus mostly on Trunks and Goten

Chapter 1 – The Daily Ritual

Two half-saiyans, one with dark volumous raven hair, the other with clean cut and thin white-lavender, were situated on opposite ends of a large forest clearing. The Raven haired half Saiyan stared down his best friend-turned-temporary-opponent, his dark eyes focusing intensely on the Saiyan Prince's movements looking for any pretense on the princes part to attack, or any possible opening he himself could exploit. His concentration was absolute at this moment, something that had been hard for him to do lately. He slowly opened his fists then clasped then shut again, ensuring they were ready for what was about to follow. The two had finished their warm-up and were ready to go all out.

His opponent, the light lavender haired half-Saiyan prince, Trunks, returned his friend's intense stare, mentally ensuring he had correctly followed his father's 30 something step checklist about engaging a worthy opponent.

This scene was not at all uncommon between these two; in fact it'd become something of a near daily ritual. Come rain, snow or storm, they'd make their way to this clearing, or another like it, in the late afternoons, ready to engage in the nearly 20 year old rivalry aspect of their friendship-rivalry duality.

Trunks had noticed his friend had begun to slip the last few weeks. That's not to say Goten made for an easy opponent; quite the contrary. At their maximums, Trunks knew he only just nudged out his best friend in skill and power. But rather, Goten's concentration and skill seemed to falter at key moments, allowing Trunks to easily get the upper hand. Granted Goten usually didn't take training as seriously as Trunks, and usually trained more for fun and relaxation then to develop strength and skill like Trunks and his father; but most of Goten's lapses had occurred while fighting. That was an area Goten and his father Goku were usually just as serious and focused as Trunks and Vegeta. Trunks knew Goten and Valese were having problems, but Goten's fighting had never been affected by a girl before. Maybe things were a lot more serious with Goten and Valese then Trunks thought. Goten wouldn't talk about it of course, and had met Trunks' questions with an insistence that everything was fine. If Goten didn't want to talk about it, there wasn't a whole lot Trunks could do about that. When they were little, Trunks could have pummeled or tickled Goten into surrendering his secrets, but that didn't work so well anymore. All Trunks seemed to be able to do now was let Goten know he was there if Goten did "decide" something was wrong.

That's why Trunks had found today's match unusually exhilarating so far. Goten's focus, timing and skill seemed back to their old levels, and it was giving Trunks quite a large amount of difficulty. He wasn't sure what had gotten into Goten today, but he was glad for it, and would be sure to probe for the answer later. For now though, he was just determined to fight this fight to its fullest.

Trunks twitched slightly amidst his thoughts, his right hand pulling up slightly.

"Gotcha!" Goten thought, a smirk on his face as he rushed the few feet across the clearing, pushing the grass and tree branches behind him back from the force of his forward rush. Goten had noticed that slight fidget and knew that for the briefest instant, Trunks' right side was vulnerable. He pulled back his right arm across his chest, fist clenched tightly. Trunks raised his right arm in defense, but was not able to readjust his ki quickly enough. When Goten swept his arm forward, it collided hard with Trunks deficient defense, easily toppling Trunks from where he stood his ground and launching him into the tree line.

Trunks quickly pulled his arms and legs in tightly towards his body in an attempt to reduce the number of trees his body tore through. He felt the trees buckle and break beneath him before he flared his ki enough to bring himself to a near stop. As he did so he saw an opportunity. He allowed himself to drift into a massive nearby tree. He braced his feet firmly against it's trunk before flaring his ki further and launching himself forward. The bark and parts of the tree beneath his feet practically disintegrated in a hail of debris as he rushed away from it. It was easy to rush his way back to the clearing, his body had cut a pretty noticeable swathe of destruction in the forest. He smirked slightly, happy that Goten had actually got the jump on him there. It meant Goten really did have his finesse back. As the clearing came back into view, he saw Goten was ready for him. Trunks was unsure if he had the momentum to knock Goten over at this speed, but decided he'd give it a try. He raised his arms defensively, forearms crossed in front of his face just before be reached Goten. Goten seemed to have decided to try and stand his ground rather than try and dodge the rapidly incoming Trunks; he had braced himself firmly in the ground, hands raised to meet Trunks.

Trunks slammed into Goten, sending a powerful shockwave emanating from the spot. The shockwave rapidly spread out, disturbing the forest in every direction and only aggravating the already rapidly growing faults in the ground beneath Goten's feet. Goten had met the attack well, having only been staggered back slightly. However the ground beneath his feet was rapidly failing beneath the enormous force needed to keep back Trunks. The two were staring at each other intently between their locked arms and hands, their Auras battling each other and refusing to give up and inch just like the two of them. The fissures beneath Goten's feet and Trunk's aura were rapidly increasing in size and number and Trunks could feel Goten about to slip once his footing failed him. Trunks flared his ki out slightly stronger, but the added force was enough to cause Goten's footing to fail. As Goten attempted to readjust to the lack of ground beneath his feet, Trunks quickly pulled back from Goten, removing all the resistance to Goten's forward push. Though Goten quickly recovered from the rapid changes in his position, momentum and velocity, it was not quick enough to brace himself for Trunk's attack. Trunks had pulled back from Goten and rapidly extended both feet forward with an upward angle. His feet struck the unprepared Goten's chest and had launched him skyward. Trunks rushed after Goten, streaking blindingly fast out of the clearing and towards Goten's tumbling body. He pulled back a fist, ready to strike Goten, but just as he reached Goten, Goten seemed to just vanish, and Trunks' fist careened through nothing but a faint remnant of the Saiyan who'd formerly occupied the space. This sort of quick speed burst was common, and Trunks braced his body, expecting a strike from Goten to come a second later, but it didn't. Trunks realized he actually couldn't sense Goten's energy. That didn't seem right though. Sure Goten was fast, but fast enough to pretty much instantly move out of Trunk's detection range? That didn't seem right. Trunks looked to the forest and clearing below, his sensitive Saiyan eyes piercing deep into the underbrush, but not finding Goten. As he continued his search, he felt a sudden spike in energy behind him. Trunks spun around quickly, raising his hands to engage Goten, only to see that Goten had his hands back, clasped around a swirling mass of blue energy. Trunks did a double take, trying to back away from Goten as Goten began the final stage of his attack.

"HAAAAAA!" Goten roared, pushing his hands forward, and unleashing the swirling pool of energy. As it left his hands it burst forward into a massive wave, radiating intense blue light and energy that set the surrounding air, land and water alight.

Trunks cringed as he rapidly attempted to bring his hands up to mount some sort of defense, knowing it was too late to try and avoid the attack. Regardless of what he did, he knew this one was going to hurt. The front of the Kamehameha wave slammed into trunks, briefly inflecting and slowing as it battled against his aura and ki. Trunks felt the heat and energy of the wave as his attempt at defense rapidly crumbled and the wave enveloped him. He let out a slight cry of pain between clenched teeth. He was desperately trying to keep his body rigid and braced against the attack like his father had taught him. But it was incredibly difficult. Although Goten had only unleashed the wave for several seconds, it had felt like a much longer time for Trunks. When Goten finally did end the wave, dropping his hands to his sides, the two were both clearly winded; Trunks had definitely gotten the worst of it, the tips of his hair and clothes slightly scorched and blackened, and his breathing more labored and deep then Goten.

"Heh, nice one Goten.." he managed to spit out. Though he was rapidly catching his breath, it was still a slight struggle to breathe.

Goten grinned his usual goofy grin (the grin being something of a Son trademark, given his father and brother often mirrored that expression).

"I thought you might like that one." He said coyly.

"How did you get away from me so fast?"

"Maybe you're just getting a little slow in your old age Trunks." Goten jested, his breathing having slowed to almost normal levels.

"Yea yea." Trunks said dismissively, brushing back a few strans of hair that had become loose and rolling his eyes. "Seriously though."

"Well you're not the only person who trains with their dad." Goten said, a mischievous glint in his eye.

"Instant Transmission." Trunks sighed, half annoyed and half impressed as he crossed his arms. "I shoulda known. You know that won't work on me again though, right Goten?" Trunks asked, moving back into his fighting form.

Goten's grin grew slightly, narrowing his eyes as he moved back into an attack stance as well. "Well, let's see Trunks."