Hakai Me no Yuuri - Chapter 24: Let’s Form a Brigade

What is my 1000-year-old monster self to do when I’ve failed my immortal ascension? Time travel — accidentally — and wind up back in my 9-year-old body, needing to re-cultivate, of course. But after that? Get REVENGE! Muahahahaha! But the idiot who killed me — also accidentally — was the main character of the dumb harem Xianxia I transmigrated into. But wait. Wasn’t he only 7 or 8 at this point in time? Well, since I can’t harm a child or the main character without suffering in some way, then I’ll just have to raise him better, faster, stronger, and loyal! Muahahahaha!

James Ye is a son-in-law everyone looks down upon, but no one knows his true identity is that of a young master from a top family.Those who scorn him will ultimately kneel before him, calling him 'Master' in awe and fear!

Chen Yan travels between worlds, ending up becoming an honorable prince in a medieval fantasy world. Yet this world was not quite as simple as he thought. Witches with magical powers abound, and fearsome wars between churches and kingdoms rage throughout the land.

Roland, a prince regarded as hopeless by his own father and assigned to the worst fief, spends his time developing a poor and backward town into a strong and modern city, while fighting against his siblings for the throne and absolute control over the kingdom. Join Roland as he befriends and allies with witches and, through fighting and even farming, pushes back invaders coming from the realm of evil.

- Description from Novelupdates

This is a world where a king is the most powerful.