@Lunis
I actually spent a lot of time discussing this with my friends back when I played this as a teenager. I recall this about the game.
- Humans in a colony ship crashlanded on the Xenogears planet in the distant past. This is why it has the cool dystopian setting... kinda.
- Ellie and Jan(whatever his name was, main character) have some kind of direct genetic relation to the original survivors of the crash.
- They reincarnate every so often and have done this through many civilizations that have risen and fallen.
- Mechs are weapons of choice but are generally relics of a bygone era. But they can keep making them, just not to the original quality.
- This is why Jan's crew gets super-mechs when they interact with the ancient anima-tech.
- Some people have also survived through the epochs and recognized that Elly and Jan reincarnate and they are important to... stuff
- The enemy behind everything is this guy. As he orchestrated absolutely everything to achieve his goal. Krellian was a pretty cool enemy.
- Krellian converted himself to nanomachines to become immortal and that guy Gan was a Jan from the distant past who was also immortal and insane.
- Something something Krellian triggers the apocalypse and shit and kills off a bunch of people and the immortal Cain who was the leader of technologically advanced humans and connected to machines. Krellian created that knight guy as a clone of cain just so he could kill Cain. As nobody else had the power to get close to him for some reason.
- World goes batshit
- You fight a machine called God in the ruins of the crashed colony ship
- ????????
- Game ends.
The reason japanese stories are like this is because of their preference for Aspect to Aspect storytelling. They don't really care about a linear story.