MTL - Legend of Swordsman - Chapter 3144 kill!

Damian, a Centurion of the Punishment Unit of the Baroque Kingdom. “Damn it.” Just once. If I were given just one more chance… ‘I would have truly conquered the battlefield with these guys.’ At the age of 30, he closed his eyes on a nameless battlefield. But when he opened them, he found himself back 17 years in the past. And this time, he had a perfectly functioning mana core that could wield magic. ‘This time.’ I will rise higher than anyone else. I won’t be swept away by the turbulent times. ‘I will conquer.’ Damian, who has returned to the past, wields his spear toward the world.

I’ve reincarnated as the reverse harem game’s villainess, the one and only step-daughter of the Eckart duke family.

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

This stands at the forefront of strategy guides to Life (a shitty video game)!