A small reality check, the typical modern person (especially Japanese would not be able to survive in this type of culture. Especially if they did not have an "OP" ability.
Not only would they stick out like a sore thumb, but they would be taken advantage of and most likely lose all their money and their freedom before they realized that "primitive" times are much harsher than they realize.
Hiding their "true strength" isn't a bad idea at the least, I found that logical and thus entertaining.