So the idea behind this story is that somebody gets reincarnated as a Necron or Eldar in 1,000,000-50,000 BCE with a system that if you collect the body of someone allows you to steal their intelligence, strength (anything and everything physical thats good like reflexes, phisical strength, muscle memory, etc), skills, knowledge (not memories), abilities (of any kind), and any thing else you can think of.
The system can also give OPTIONAL quests. If you do things like collecting artifacts, kingdom building, learning new things, getting stronger, and more, you can get rewards like a "card" of, for example, John wick, bear grills, etc. The quests would give you rewards somewhat based off the activity.
The system could also have features like the ones from Total War system: Stuck between DC and Marvel, such as the war room, but it's more kind of a map and as the MC progresses and expanded so too does the map, like if you expand to a new area or map most of an area it unlocks on your map and if you move into space it's the same thing but the map expands by 2 astronomical units from the area you map or expand too (it would just map the general shape of a planet, you would have too map or expand to individual planets).
The highest rewarding quest or thing to do is anything that help humanity as a whole, like advancing technology, letting humanity evolve, stopping crime, solving world hunger and climate change, and just things like that.
Anyway, I'm going to stop here since it's currently 4:09 AM and I'm really tired. if you want to use these ideas, you can, and although I would appreciate it if you credited me for the idea, you don't have too it's all up to you. :)