and the education, too. if they were older and studied in korea, even if they were to be given a "royal's education", they'd still have at least some knowledge, and the teachers would at least be a little bit confused as to where they learned things like multiplication or whatever. instead of always being behind, i would think they'd be fast learners, since as they go through their work, they'd remember, at the very least, bits and pieces of what they learned in school, even if it hadn't been put into practice in so long.
exactly! even if they weren't the greatest at studying when they were in Korea, it doesn't mean they completely forgotten the fundamentals!
I really want the pair to be thoroughly happy and enjoy life as much as they can after years of abuse but :( their reincarnation isn't playing an important role. even though their mental age is brought up often, there is nothing else.
it has occurred to me that they haven't really called each other by their original name. you would think it would slip in their telepathic combos but it doesn't. there are no callbacks to personal details of their previous lives. all we know is that they used to live in a modern era and that they were Korean twins that died because of "certain reasons." they don't think about their family and friends, nothing reminds them of their past lives; like they've detached from it completely. especially considering the abuse they went through. alright... maybe they didn't have time to think, just survive but when they are given the chance to, how could they not feel an incredible sense of loss? the loss of a normal childhood, caring parents, close friends. hell, even the nights they've spent studying, working or any sense of normality. their connection to anyone and anything they used to do and love stripped from them and now, they only have each other to rely on.
possibly, it's too early to tell whether or not it's going to come into play. I hope it is. otherwise their mental age is just an excuse to have 'mature' children rather than 18 year olds in a child's body.
tl;dr the MCs are pretty shallow as characters, they don't have the depth reincarnation allows them to have— it's just a device to let them act a more mature compared to a normal child.