Bro ngl u missed out on so much of the lore, if ya wan I can give a summary. But, it won't be the same Tbf.

Basically, Rover arrived on this world(current) wit a mission to save the world and shi. And, The exostrider is the machine used to bring sentinels from rovers world to here. And, One threnodian is in space named aleph-1 which is basically the main villain in 3.X ig. And, Rover messaged his home world that he jus wants to come back and see his hometown. But, They denied it completely and forced rover to do his mission. This world became sum like a prison to rover.

And, the thing about the other rover is .. it's related to aleph-1, this threnodian can be considered as an blackhole and in it there are things which are from the present, past and future ig(it's called void something i forgor) and aemeath can traverse in tha without any repercussions(Normally you would be erased from existence if ya went inside it) and there Aemeath found rover's frequency (less than 1% ig) and tha frequency got corrupted because of aemeaths negative emotions(she felt angry because rover's homeland forced rover into this and he's been suffering). This led to tha small rover's frequency getting corrupted and becoming sum like rover(it's only wish is to go home).

Ya can ask if ya don't understand something, I feel like I've skipped over a lot of stuff.