@Mr.Toilet if the laws in that fantasy world are exactly the same as they were in IRL Korea then the only way for MC to have a legitimate relationship with these royal concubines is if he himself becomes the Emperor, which is only possible if he starts a rebellion and overthrows the current ruling dynasty (which is exactly what his father tried to do and failed). It doesn't matter how much he may rise in rank, royal concubines are the property of the Emperor/Crown Prince while also technically being a part of the royal family, they can't be in any romantic or sexual relationship with anyone else. These women are born into their position as royal concubines and there is pretty much no legitimate way for them to be set free. Technically the Emperor can relieve them of their status as royal concubines, but usually when that happened the concubine in question first lost the Emperor's favor and even after being relieved of her status was still confined to the palace.