One possible fanfic could be about Goku's intense training before the Cell Games. He might be shown pushing his limits in the Hyperbolic Time Chamber, trying out new techniques and forms to defeat Cell. Maybe he discovers a new power level that no one, including himself, expected.
It could be someone from Goku's past who has a vendetta against him and takes advantage of the chaos during the Cell Games. For instance, an old enemy who was thought to be defeated but managed to come back stronger and wants to finish Goku off while he's weakened from the fight with Cell.
One common theme is the clash of ideologies. Goku is all about protecting the innocent and having a fair fight, while Cell is more about self - preservation and domination at first.
In the manga, Goku has experienced death multiple times. However, his death is often a part of the narrative and doesn't mean the end for him. Resurrection and comebacks are common in his storyline.
In general, it's a bit of a toss-up. The strength of Manga Goku and Anime Goku can vary depending on the specific arcs and battles. Sometimes, it might seem like one is stronger in a particular situation, but that could change in another.
Perhaps a rogue Saiyan from another part of the universe. This Saiyan has heard about the Super Saiyan powers on Earth and wants to prove his superiority. He shows up at the Cell Games and challenges Goku and Gohan. He has a different fighting style, more brutal and less honorable than the Saiyans on Earth. His presence adds a new layer of conflict as Goku and Gohan have to decide whether to fight him on his terms or uphold their own values.
One possible plot could be a story where Goku meets a female version of Cell who has different motives than the original Cell. Maybe she doesn't want to destroy the Earth but instead is on a journey of self - discovery. Goku, being the protector, is initially cautious but then starts to see her potential for good.