I gotta give mad props to the girls, even I don't think I could keep up such a convincing act as they did for three whole years without attracting some suspicion until the last day.
Also wtf, I don't get why they wouldn't defect or something because of his charming manga MC characteristics, they were with him for 3 whole years, and on the last day, they showed guilt, so I don't get why at least one of them wouldn't do something, like almost tell him but stop themselves, of course, the bad heroes could just be threatening them or something, "subordinates" could mean a lot of things for them, or they could really hate him being overwhelmingly stronger than them, speaking of being stronger than the others, isn't using multiple elements kind of broken for one element to be able to do? And why darkness? Wouldn't it make more sense for wind to be able to manipulate certain elements?
Also, why are the attribute heroes stronger than the element heroes? Well i mean there isn't any book saying that they have to be or something, its just that you would think that people given the power of an element would have more things that they would be able to do with that power, its an entire element (of course it could just be elemental magic, which would explain a lot, but idk), versus a single attribute, like better sight or speed.
Of course, if i sound like i think the author is bad or a terrible writer, I don't think that, my mind just works very logically, so I pick out all the logical problems with a narrative when i see them, everyone has their own way of writing (and drawing), and my overly logical way is definitely not the only way to write a good story.