Who could be the main antagonist in a Gundam Seed Shinn time travel fanfiction?

Well, one possible plot could be that Shinn travels back in time to the start of the war. He uses his knowledge of future events to try and prevent certain tragedies. Maybe he tries to stop the development of some of the more dangerous mobile suits. He could also attempt to change the relationships between the different factions, like trying to make the Earth Alliance and ZAFT cooperate more.

It could be a rogue scientist who was once part of the Gundam project. He has his own ideas about how the Gundam technology should be used and is willing to do anything to get his hands on it, even if it means going against Sonia and the Gundam's pilot.

It could be a time - traveling sorcerer who wants to change history for his own evil purposes and sees Achilles as a threat. The sorcerer might try to stop Achilles from getting back to his own time or use his knowledge of the future to his advantage against Achilles.

Perhaps an ancient evil that was sealed away long ago but is released due to Temari's time - traveling disruptions. This evil entity then starts causing chaos in the past, and Temari is the only one who can stop it with her modern skills and knowledge.

A time - traveling bounty hunter could be the main antagonist. He might be after Lucy because she has somehow disrupted the time - space continuum. He's cold - hearted and will stop at nothing to bring her to some time - traveling justice.

Cell could be a great antagonist. Imagine Goten travels back in time to before Cell was complete. Cell could sense Goten's power and try to absorb him to become even more powerful. This would put Goten in a tough situation where he has to avoid Cell while also trying not to disrupt the timeline too much.

It could be a time - traveling villain who is trying to disrupt the timeline for their own gain. This villain might be trying to erase certain events or people from history to change the future in a way that benefits them.

It could be a time - traveling villain from the future who wants to change the past to gain more power in their own time. They might try to stop Naruino from achieving their time - travel goals.

It could be an older version of Orochimaru who has also found a way to time travel. He might try to change the past to his advantage, like getting rid of the Third Hokage before he can become a threat to his future plans. Orochimaru is always power - hungry and his older self could be even more dangerous with knowledge of the future.

It could be a future version of Orochimaru who has found a way to come back even more powerful. Maybe he has developed some new form of immortality and is causing chaos in the future world that Naruto travels to.