They could time travel to the future where a new and more powerful enemy has emerged. Goten and Trunks find that their future selves are not strong enough to defeat this enemy. So, they come back to their present time to train harder and also bring some knowledge of the future enemy's weaknesses. This would involve a lot of self - discovery for them as they realize they need to grow much stronger.
One interesting plot idea could be that Goten and Trunks travel back in time to the Saiyan - Vegeta and Goku's father Bardock's era. They could end up changing some events that lead to a different future for the Saiyans. Maybe they prevent Frieza from destroying Planet Vegeta in a more creative way than expected, like by using some future technology to make the Saiyans seem more powerful than they actually are at that time.
One idea could be that Goten and Trunks accidentally travel to an alternate dimension where their roles are reversed. Goten could be the more studious and reserved one while Trunks is the carefree fighter. They have to figure out how to get back while also dealing with the differences in this new world.
One idea could be Goten traveling back to the Saiyan - Saiyan war era. He could end up changing some small events that have big impacts on the future, like uniting some Saiyan clans earlier. This would create a whole new timeline where relationships between characters are different.
One idea could be Future Trunks bringing back a technology from the future that changes the course of the present timeline's battles. For example, a more advanced scouter that can detect hidden power levels more accurately.
Another idea is Goten traveling to the time when Goku first arrived on Earth. He could interact with a younger Goku, Piccolo, and the others. He might accidentally change the way Goku grows up, for example, by introducing some new training methods he learned in his own time. This could lead to Goku becoming even stronger much earlier and changing the battles against the Red Ribbon Army and later villains.
Their relationship could also become more of a mentor - mentee type situation at times. If they travel to a time when one of them has more knowledge about what's going on, say Trunks if they go to a time related to his future knowledge, he could be like a mentor to Goten, guiding him through the situation. But then in other situations, Goten's natural fighting instincts might lead and Trunks would learn from him. This back - and - forth would change their relationship in a dynamic way.
Perhaps there is a situation where they have to team up to protect the Earth from a new threat. In the process, they discover feelings for each other that they hadn't expected. Their relationship then develops against the backdrop of this high - stakes adventure.
One interesting plot could be Trunks and Goten going on a time - traveling adventure together. They could visit different eras in the Dragon Ball timeline and encounter various versions of their family and friends. Maybe they end up in a timeline where the Saiyans never died out and experience a whole different Saiyan culture.
One possible plot could be that Goten and Future Trunks meet during a time - traveling accident. They initially have some misunderstandings due to their different upbringings and experiences. But as they start to train together, they learn from each other's fighting styles and develop a deep friendship. They then team up to face a new, powerful enemy that threatens both their timelines.
In such fanfictions, one characteristic could be the exploration of new character dynamics. Since Goten and Trunks are usually depicted as friends or comrades in the original series, a kiss in fanfiction would likely change the nature of their relationship. The stories might also focus on how their friends and family react to this new development. Another aspect could be the use of vivid descriptions to convey the emotions involved in that moment of the kiss, whether it's surprise, confusion, or a long - hidden love finally being expressed.
Some fanfics might focus on how they handle the challenges of being half - Saiyans in a unique world created by the author. For example, they could be dealing with new enemies that only target Saiyans and they have to rely on each other's strength and their bond. This can lead to some really intense and exciting plotlines.