Well breed up one's army via various breeding strategies.
However after one reaches a certain level, able to clear dungeon, it totally loses purpose
Well... An army is only needed because there are births, and these offspring need to be disposed of somewhere (selling is possible, but an army is more practical). And they can also bring captives, which provide some resources. True, the captives are so-so; I remember I assigned all the named girls to a brothel—perfect for making money

And the strategy is basically the same: a girl with high stats is born—we replace her, sell the old one. Then we repeat as often as necessary. Until monsters with stats capable of destroying a planet grow. But there are no such places in the game (well, maybe only a dungeon, but I'm not sure. Or maybe the developer added something else, I don’t have enough information, I don’t play it anymore).