Concept:
MC is a robot who's goal is to assimilate every being into his own, for they shall work for him. Maybe also to explore the world/galaxy?
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Background:
Yours to pick. I suggest fantasy or cultivation as it might be more interesting. technomagic? spiritual technology? All for your choice to pick!
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MC's background:
Like I said, I am just giving suggestions so, reincarnation might work. Or an actual robot who is lost from his galactic empire and crashed into a random world with his science ship equiped with the basic needs to perform research and make other living beings into one of him.
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Romance:
No, just no, heed my advice as romance will f*ck this story up. You can add it, but if you also decide to add harem then you can basically already stop the idea of writing this story.
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MC's personality:
Cold is highly recommended from me. But comedic is also fun.
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Add a system:
System is really an easy template to work with and certainly works with this idea. But your choice.