The supporting character's harem is very normal - Chapter 474 Peace before the Storm

Min's system, System #151044, is tired of watching him get girls and make dumb decisions yet still manage to defeat the villain. If only he was the villain, there's no way Min would win.

His wish was granted. He now upgraded from a bodyless helper system to the evil villain, Ronin Dreadborne!

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After getting murdered and reincarnating as a system inside a Hero Transmigrating Machine, System #151044 spent thousands of years wondering why he had such a cruel fate to be a system for incompetent transmigrators like this.

But the worst is Min Cheng............

Because Min Cheng spends all his Hero points on girls instead of leveling up! And he is the dumbest transmigrators he ever met!

But through a rogue system that gave them a code to free themselves from their roles as a system, System #151044 was able to transform into Min Cheng's enemy on the next world, Ronin Dreadborne, in a mage fantasy world!

[Fate itself is evil. The only true enemy is fate, and I have defeated it.]

[And I shall teach you how to defeat it too. I will be giving you the gift of freedom. ]

[Be the master of your fate like you were always meant to be. And conquer those who try to stand in your way.]

That is exactly what he did as Ronin, and to defeat an evil fate, you have to be evil yourself!

“I will be the best villain in all the dimensions! Watch out, Min Cheng! I'm coming for you!”

Our protagonist Caam is a man from Earth that was reincarnated into this world as a demon. In order to survive, he spared no effort in avoiding the sparks of battle and without noticing it, he became strong himself.

Lyle Walt is a young noble boy and heir looking forward to the day he can inherit his family’s territory. Except around when he was 10 year old, his parents started neglecting him more and more in favour of his little sister, Celes.
On his fifteenth birthday, he is challenged to a duel by his sister to see who will inherit the household and horribly loses, being cast out of his family. Afterwards, he gets treated by the family groundskeepers and receives the family heirloom Gem from him that Lyle’s grandfather had entrusted to him. From there, he begins an aimless journey with his childhood friend and former fiancée, Novem, and the Gem-turned-Jewel that houses the memories, personalities, and Skills of seven of his ancestors.