The supporting character's harem is very normal - Chapter 219 New Contract

The journey of a generation’s male empress started because of four words.

“Send a dowry escort.”

During the 19th year of Yuanqing, Qi Yunruo boarded a carriage and entered through a corner door of the second prince’s estate. Then, across the watery corridor, he gazed at the prince from afar.

Notes:

For aristocratic women in imperial China to marry into a family part of the upper nobility, they must be of the legitimate line and must also have an escort/dowry maid that married into that family. That escort would be a “ying” (媵) and could be considered a concubine.

- Description from Novelupdates

Ou Renjin likes keeping beautiful young men because he likes watching the drama.

Watching them be arrogant and conceited; watching them be obsequious and sycophantic; watching them have ulterior motives and fight with each other, seeing all the evil side of human nature.

Until, he picks up a poor little guy.

The poor little guy is ignorant and helpless, treating Ou Renjin as his whole world, spending all his salary to buy him gifts, standing in front of him in times of danger without hesitation, even…

…saying to him in the calmest and lightest of tones after knowing that their heart matching is successful, “I am very grateful that you have been hiding it from me, but I have long been ready to give my heart to you.”

* * *

036 was born as a test subject, without parents or friends.

As the only successful “petri dish of renewable organs”, he had every organ in his body cut out and transplanted to the rich and powerful countless times.

After getting used to the pain, he met the most special person in the world.

This person was so good that he wanted to cut out his own heart immediately.

- Description from Novelupdates

The Venerable Xiang Yu, an eccentric villainous half-blood demon King was infamous in both the demon and human realm for being a cold-blooded ruthless devil that could kill with no remorse.Demons and humans feared him, cultivators wanted him as a trophy and the immortals saw him as a thorn in their side.The only reason he didn't get smote by the Heavenly King's searing lightning of divine wrath that could kill all mortals and immortals was because he kept the deadliest demons in check maintaining peace between the two realms.Despite his reputation, he had a small cult following in the human realm. They took him as their deity for his selfless acts of benevolence.Such rare selfless acts led him to rescue the fallen immortal Han Xin. But his benevolence became his downfall. Condemned to death, he faced an impossible choice: serve the Heavenly King or die with no marked grave.Xiang Yu: Hahaha... death isn't so bad after all.Heavenly King: You...Han Xin: Wife, you can't escape even in death. At least when you are alive you have a chance to run.Xiang Yu: QAQ...