Another option is a crossover with a different anime world, like Naruto. GT Goku could end up in the Hidden Leaf Village. The shinobi would be amazed by his power. Goku, being Goku, would be interested in learning their ninja techniques. They could team up against a common enemy that somehow has the ability to use both chakra and ki, creating a unique and exciting battle scenario.
One key moment was when Chichi first declared her intention to marry Goku when they were kids. Another was when Goku finally agreed to marry her. Also, every time Goku returned home safely from a battle, the warm reunion with Chichi was a significant moment in their love story.
One important moment was when they first met. Bulma was looking for the Dragon Balls and Goku had one of them. It was the start of their long - journey together. Another moment was when Goku transformed into a Super Saiyan for the first time. Bulma was there to witness this amazing power and it changed her perspective on Goku's potential even more. Also, when they fought against Frieza together, with Bulma providing crucial information and Goku doing the fighting, it showed how well they worked as a team.
One epic scenario could be Goku achieving a new form even more powerful than Ultra Instinct. He might use this form to battle an ancient and extremely powerful evil that threatens the entire multiverse. This new form could have unique abilities like the power to manipulate time and space at will, allowing him to outmaneuver his opponents.
Perhaps when Naruto faces Itachi in the Akatsuki. Itachi, with his powerful Sharingan, would be a tough opponent. But Naruto, with his unwavering belief in his friends and his own ninja way, could break through Itachi's illusions and attacks. It would be a battle of wits as well as strength, and Naruto's victory would be a huge moment in the fanfic.
One of the most epic moments could be when the main characters use their ultimate magic in unison. For example, Natsu might combine his Fire Dragon Slayer magic with Lucy's Celestial Spirit magic for a super - powerful attack against the enemy.
One epic moment could be when Naruto first enters his nine - tailed fox form. The chakra surge would be huge, and the area around them would be filled with a menacing red glow. Whitebeard would have to brace himself as Naruto lunges forward with enhanced speed and strength. Another moment could be when Whitebeard uses his quake - quake fruit to create a massive tsunami - like wave of destruction, and Naruto counters it with a huge rasenshuriken, the two powerful attacks colliding in a spectacular display of power.
Definitely include Bardock's last stand. His heroic yet doomed battle is a crucial part of the Saiyan lore. It could be written in great detail, with Bardock using his full power against Frieza's forces.
One epic moment could be when Igneel unleashes his most powerful fire attack, a huge blaze that engulfs the area, and Acnologia just withstands it with his dark aura. Another could be when Acnologia lunges at Igneel with his massive jaws, and Igneel dodges at the last second.