5 years before Goku's birth
Trunks flew across space, having just stopped another planet's war. He had liberated many worlds from tyranny since leaving Earth, becoming a legend across the stars. He had liberated planets like Wisp, Power Star, Coruscant and many others. But there was one planet that he had waited until now to visit.
Planet Vegeta. The birthplace of his father and stepfather, and the home of the soon to be extinct saiyan race. He knew that Frieza and King Cold would likely be here, and this could be his chance to not only save the species and put them on a better path, but he could also stop Cold and maybe give a young Frieza a chance of redemption.
It was what Jesus would do, after all. Trunks quickly noticed a hoard of ships orbiting a red planet, and deduced from the powers he could sense on it that it had to be Planet Vegeta. He suppressed his ki as low as he could and flew down to the planet's surface. On the surface, King Cold was telling the saiyans,
"I'm retiring, effective immediately. From this moment on, Frieza will be your commander. In other words, the Cold force has now become-"
Before Cold could finish his sentence, Trunks landed in front of him in a flash, causing a small explosion as he impacted the ground. As the dust from the impact cleared, the half-sayian stood up. Everyone was shocked at seeing this random purplish-black haired humanoid wearing strange robes suddenly land in front of them without anyone detecting it. Trunks stared King Cold down and ominously said,
"King Cold. I've come here to kill you."
King Cold laughed a little at this. He asked the half-saiyan,
"You think you can waltz onto one of MY planets and get away with it, you cursed inteloper?"
The king turned to his son and asked him,
"Frieza, be a dear and check his power level for me, will you?"
"Yes, daddy."
Frieza motioned one of his soldiers to open a briefcase he was holding, and the soldier did so. Within the briefcase were devices unfamiliar to the saiyans watching, but very familiar to Trunks. Scouters. Frieza put one of them on and scanned Trunks's power level, smirking confidently when he saw the number.
"No need to worry, daddy. This fool only has a battle power of 800. I'll dispose of him."
Before Frieza could even think of lifting a finger however, Trunks rushed at him faster than anyone could see. Within a tenth of a second, Frieza and all the other soldiers were unconscious on the floor, and Trunks was standing where he had just been before, smirking. If he had had the mentality of his younger self, Frieza and the other soldiers would've been dead.
But being with Jesus in person for so long had taught him the value of sparing others and showing forgiveness. However, he knew from what he had watched King Cold do over the years that he was too awful to be forgiven. Trunks silently whispered,
"Lord, forgive me for what I must do."
Trunks drew his sword, and King Cold smirked.
"Not bad for a lowly humanoid. But what makes you think that I'll even have to lift a finger to kill you?"
"I am Trunks, the hero of the stars."
"WHAT?!"
King Cold was all too aware of the legendary hero of the stars. Said hero had slain his ancestor Chilled over a thousand years ago when he had tried to invade Planet Vegeta back when it was known as Planet Plant. He along with Majin Buu and the "god" of destruction Beerus were the only beings that Cold feared. Cold shook a little in fear, but then recomposed himself and told Trunks,
"Well Mr Hero of the stars…let's put that suggestion to the test."
Cold suddenly fired a full power ki blast at Trunks, causing a massive explosion that blew the saiyans and unconscious villains far away, leaving only a massive crater right in front of the saiyan castle. As King Cold stared at the dust, waiting to see if he had done it, there was a nervous tension in the air.
Unfortunately for the emperor, once the smoke cleared, Trunks was still standing there, completely unfazed. King Cold flinched in surprise at this, but then said,
"So it seems you're the real deal after all. Well then, I suppose I should honor the legendary hero of the stars by showing him my absolute full power!"
Cold then began powering up, his purple aura casting an ominous purple light and causing the entire planet to shake. However, Trunks stood like a statue, unworried by the power being displayed, even as it climbed higher and higher. Eventually, after a few minutes of powering up, Cold let forth a huge surge of ki as the transformation completed.
Trunks observed his foe. He appeared very similar to Frieza's final form, but he was much more muscular, taller, and the gems on his body were a cyan color instead of purple. Smirking, Cold told Trunks,
"You should be proud of yourself. Not even my sons have seen this form. I may not be as strong as Beerus or Majin Buu, but I'm still more than enough for the likes of you!"
Trunks stared at Cold's new form, and after a few moments of deliberation, said to him,
"I'll only need a percent of my power to crush you."
"DON'T GET COCKY!"
Enraged, Cold charged at Trunks and threw a punch at him…only for the future warrior to not even flinch at it, even as it impacted him. Cold was left in shock, and Trunks then began laying a merciless series of blows on him. Each punch sent Cold flying through buildings and dealt a massive amount of damage.
After 3 massive impacts, Trunks wound back his fist as holy white energy began to encircle it. The heroic half-saiyan then let out a shout of,
"HOLY FIST!"
The attack struck Cold in the stomach, causing the king to feel more pain than he ever had before. As he struggled on the ground in pain, Trunks looked down at him coldly. Cold stammered out towards the future warrior,
"P-please…let me go….I'll never….hurt anyone…..again…."
Trunks for a moment considered doing what Cold said. It was what Jesus would do after all. But then he remembered his mother telling him about his father's battle with Frieza, and about how he had tried to let Frieza go, only to have his mercy turned on him. Trunks knew deep down that Cold would do the same.
"I'm sorry. I can't let you live."
"NO! PLEASE! I-!"
Before Cold could continue his begging, Trunks held out a hand and fired a ki blast at the king, completely oblitarating him. It was at that moment that Frieza finally woke up, and as he got up to attack Trunks, he saw his father being incinerated. Shocked, Frieza asked,
"Daddy?"
Trunks then turned to the Frost Demon and told him,
"Leave this planet and never come back, Frieza. I hope we never see each other again."
Frieza gritted his teeth at this random lifeform telling him what to do, but the look in his eyes convinced him to obey. Angirly, Frieza grabbed his soldiers and retreated to his ship, flying off. Trunks looked up as the ship flew off, and then turned to King Vegeta, who had landed just in time to watch Frieza fly off. Angered, the king yelled,
"Who are you, stranger?!"
Trunks calmly responded,
"I am Trunks, your highness. I apologize for intruding, but I hope you are grateful for my aid."
"Grateful?! Oh I am! With Cold gone, this universe is mine!"
"B-but…"
"And now, to get rid of my only threat besides Frieza!"
King Vegeta attempted to strike Trunks with an execution cannon, but Trunks instinctively responded with a punch…that sent King Vegeta so far away that he went flying off the planet, and Trunks knew he wouldn't be able to catch up to him before he suffocated. Sweating, the half saiyan muttered,
"Oh, what have I done?"
He then flew to the other saiyans, who were extremely confused. Now because of him, his stepfather wouldn't be born in this timeline. However, this was an opportunity. He could put the saiyans on the right course. Breathing in and out, Trunks began addressing the saiyan bystanders.
"Attention, my fellow saiyans! I am the hero of the stars! Both King Cold and King Vegeta have been slain! No longer will your careless destruction be tolerated! I will be staying on this planet for a short while to train you all and teach you the ways of Jesus Christ, so you can all redeem yourselves in the eyes of our Lord God! Any who want to oppose me…will have to deal with this!"
Trunks began powering up, and his hair flickered golden. However, he hadn't done something like this in countless millennia, so he couldn't quite manage to reach this power. To compensate for this, he continued powering up until he erupted in a golden aura. His hair was still the same shape and color as it had previously been, but he was now engulfed in a golden aura and his eyes had vanished.
The saiyans all looked on in awe at the glowing golden warrior in front of them, until one of the saiyans yelled,
"It's the legendary Super Saiyan!"
The saiyans all bowed before their new king, and chanted,
"ALL HAIL THE SUPER SAIYAN!"
Trunks sweated a bit and told the cheering crowd,
"Wait guys, I'm not the one you should be praising. The one who you should really be praising is God."
The saiyans all then began chanting,
"ALL HAIL GOD!"
Trunks smiled upon hearing this new chant.
"Much better."
It looked like there was hope for these saiyans after all. Sure, a lot of work needed to be done, but Trunks was confident that he could mold this species into an honest, God fearing species. However, he still needed Goku to be sent off planet. Thoughts for later. After all, he had all the time in the world.
Power levels
Trunks (Suppressed): 800
King Cold (Second form): 90,000,000
Frieza (First form): 530,000
King Cold (Final form 100%): 10,188,000,000
Trunks (1% power after centuries of training): 20,376,000,000
King Vegeta: 10,000
Trunks (False Super Saiyan 1%): 509,400,000,000