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Milmang created a topic of Rainbow City

So they killed his mom too! But I still don't understand the mutation thing? What do they mean? Dr Seok is a mutation that with a defect that has obsession over rocks, Major Kwak is a mutation as well , Seok got really shocked and asked him 'are you even a mutation?'... What does mutation mean here? Are they not normal humans? And who made Major Kwak the controller position? I'm sure it's not the two masters, if anything it looks like he has his own plans...