Vampire Overlord's Harem In The Apocalypse - Chapter 10: The Gas Station (I)

Xue Xi is forced to fall in love at first sight with this dangerous man on their first meeting. With death being the only other option, she makes the first move:

That lonesome night as he lays dying in the hospital, fearing of death and desiring the taste of life, his mind became unprecedentedly complex with mixed emotions.

As he transmigrates across the continent of Douqi, Gu He takes on the mantle of Alchemy King Gu He and gains an incredible power - the Ten Thousandfold disciple cashback system. This allows him to grant gifts to his disciples, which are then returned ten thousandfold.“You have gifted Liu Ling the Green Lotus Core Flame, triggering a tenfold return and granting you the mighty Green Lotus Holy Fire!” the system announces as each gift brings Gu He greater power.After three years of intense training, Xiao Yan returns proudly to the Yunlan Sect, eager to display his newfound strength.“Don't underestimate this once poor youth!” he warns his former lover Nalan Yanran. “Today I'll show you what a true genius can do!”But Nalan Yanran just smiles faintly. “Is that so?” she asks, as a terrifying Dou Emperor aura suddenly surges from her.Shocked, Xiao Yan stammers in disbelief, “How did you become a Dou Emperor powerhouse?”With an arrogant smile, Nalan Yanran replies, “With my master, anything is possible.”

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