Complex sentence: Kronos is discovered to be the first "Accumulator" sent from an alien race that drained their own natural resources, and now they seek to have Kronos drain Earth's power and return that power to their own dying planet.
Split into simpler sentences: Kronos is discovered to be the first "accumulator" sent from an alien race that drained their own natural resources. They have Kronos to drain Earth's power and return that power to their own dying planet.