Not the Hero, Not the Villain — Just the One Who Wins - Chapter 34: The Calm Before the Storm

A human from Earth is thrust into the [Hunter x Hunter] world, becoming the Zoldyck family’s defiant, red-eyed prodigy. They call me a genius and the rightful heir, but I say that’s Killua’s burden to bear.Armed with crimson eyes, and a subtle yet powerful system, I’ll rewrite destiny, upend the world, and embrace the chaos with a wicked grin.

The figure of the Armada seems to be still riding the wind and waves in the Atlantic Ocean, and the gold of South America still seems to flow in continuously. As Alfonso from the Bourbon family returns to the Royal Palace of Madrid where he was born, the story begins here…

- Description from novelbuddy

My name is Kaelith Yurei , and I am a first-year student at the Shin'ō Academy in the Soul Society. I have a friend who is destined to be quite famous in the Soul Society; his name is Sōsuke Aizen.Unlike this ambitious and idealistic friend, my goals are quite simple: through hard work and diligence, I aim to graduate and become a seated officer in the Gotei 13, from which point I will… I bounded with who!?Whenever Aizen enhances his strength, my power automatically synchronizes to match his level.Therefore, what I need to do from now on is very clear.“Sōsuke, you need to work hard. As long as you put in enough effort, I can live the life I desire!”

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