MTL - Metropolitan System - Chapter 16 Is this about?

One day, the majority of humanity had a collective thought.

‘I wish the world would just collapse.’

And then, that wish came true.

Ten years ago, Magnolia was blamed for her sister’s death and cast out of her pack. Her Alpha father’s final words “Why did she die, but not you?” drove her into exile. She lived among humans, hiding her identity, her wolf, and her pain.Now, at twenty-eight, Magnolia learns her mate is none other than Rhett Callahan , the powerful Alpha of the strongest pack and heir to a billion-dollar empire. But instead of love, he offers her a contract: marry him for one year so he can fulfill the requirements of his inheritance.Magnolia accepts to save her parents’ home but finds herself in a loveless arrangement, mocked by the pack and haunted by the past. Then Camille returns with another woman, the one he truly loves… and it’s Magnolia ’s sister, long thought dead.As secrets explode and bonds unravel, Magnolia must decide if she can forgive the mate who rejected her or burn the past down with him in it.

In this world, orphans or just anyone without any hope for this world can apply to become a “walking target”. Their sole purpose is to be a practicing dummy for the students of the sect who train to become “Demon Hunters”. These students need “walking targets” to test their training on living, walking beings of flesh and blood.
In exchange, they will be provided with food & shelter.
Their existence value is lower than a slave, but if they manage to survive a few years they can receive a life long pension.

Xiao Han is such a “walking target”. One time he witnessed a powerful Demon Hunter disposing a demon. When the demon died, a fragment of the demon that managed to escape entered Xiao Han’s heart. No one saw that, and even Xiao Han himself only felt some discomfort for an instant.

But that thing in his heart soon gave Xiao Han visions, and the first one is of a cultivation method which allows Xiao Han to absorb damage to enhance his body. A perfect cultivation method for a “walking target”.

- Description from Novelupdates

300 years after becoming a Demon King, the war angel Ansel faced a serious problem during a certain expedition.

——His halo grew out once again.

Ansel picked an auspicious place that was definitely and absolutely unmanned, and while cursing, he simply and skillfully broke off the newly emerged angelic aperture.

This thing was growing out faster and faster!

When will his undercover mission end already?!

The demon realm was divided and ruled by three kings. Demon King Saros was forced to go on an expedition with his sworn enemy, Ansel.

One day, he noticed Ansel sneaking away from everyone.

Saros decisively followed him, and was shocked to find that his sworn enemy, another demon king of the demon realm, took off a horn headband and fake bat wings. As Ansel cursed up and down, Saros watched as he skillfully removed a cute halo from his head.

This irritable, easily angered guy who loves fighting; the type that was cute when he shuts up but could make even demons angered to the point of ascending to heaven the moment he opens his mouth…

..was actually an angel???

- Description from Novelupdates