Concept:
There exist multiple primitive worlds (or a fixed amount) and the mc starts on one. He's the lord, the god as he needs to develop his own people on the planet to fight against the others.
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Background:
I basically already said it in the concept section, as for your primitive worlds, you can add all elements you want. A fantasy one while the invading world (or you invade) is a technology based one or a cultivation based one.
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MC's background:
A newly born ignorant god or reincarnation by truck-kun again!
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Romance:
I wouldn't per se recommend it but it's certainly possible. Harem is also possible but again I am not recommending harem as it's simply not designed for not experienced authors. There are millions of novels who have a good idea and it was good until they introduced harem....
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MC's personality:
Serious?
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Add a system:
Nah, it really isn't needed, I also see no point of adding one here.