The thing is, they're not former enemies. They're still current enemies that they would not accept clemency and would continue fighting had he not enslaved their lord- because they're subordinate to a higher enemy, and THAT main enemy has as strong if not stronger claim to the throne than he...
Oyakodon is a meal made with chicken and egg, which you can say is kind of like eating the mother (chicken) and the daughter (egg) at the same time.
It's kinda obvious how it's used for lewd purposes.