Adui
I still domt get how he is Epic rank already. Last author said was the demons stopped investing resources on earth as it wasnt worth the cost at that time, so they had a few months break leaving the highest possible dungeons at Rank S before and that was the sole reason MC left earth. To go disrupt, delay (or stop if possible) the demons while they are at temporal peace from the invasion. Getting S+ skills is still ok but farfetched as they have no cheat except inherent skill(which doesn't help speed up their skill proficiency). And as for their power ranking, it shouldn't even exceed S rank, because they need epic cores to upgrade stats up to epic rank and there is no epic dungeons on earth.