Sendai Yuusha wa Inkyou Shitai - Chapter 108 – Flow

In 2120, a massive gateway that connects Earth with the Otherworld replaced the Aels boulder in central Australia. The Earth, representative of science, and the Otherworld, representative of magic, subsequently made contact and two wars broke out. Both wars inflicted enormous damage on both sides, eventually leading them to choose peace negotiations, and thereby marking a thirty-year era of peaceful exchanges between Earth and the Otherworld.Even though both sides chose to coexist peacefully, they each coveted the other's benefits. With the impending arrival of the third inter-world war, Earth's Otherworld combat General Staff Headquarters decided to secretly dispatch an advance team to the Otherworld to conduct pre-war reconnaissance.As a hybrid of Earthlings and Otherworld elves, Luoer, after secretly studying and training for over twenty years in Haiya Academy, which specializes in cultivating hybrids of Earthlings and Otherworld inhabitants, will soon lead his squad into an exciting adventure in the unknown Otherworld.Swords and magic? No, this is a world of guns and magic!

It was supposed to be a perfect deal in which both parties got what they needed. However, after the child was born, he tore up the agreement with discontent and told her, “Who said that we’d only have one child? I want twins! Twin brother and sister! You’ll continue giving birth to more children until you bore me a pair of twins!”

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

At the age of 12, Naruto Uzumaki gained the extraordinary ability to traverse between his home world, the Ninja World, and the mysterious world known as the Soul Society.Naruto's DiaryKonoha Year 63, March 15: I seem to have died [crossed out] I seem to have died and come back to life.Konoha Year 63, March 16: The weight of this new existence crushes him. A return to life offers no solace, and he questions whether it might have been better to remain dead.Konoha Year 63, April 1: Desperation sets in as Naruto searches the Soul Society for his parents, only to discover that this world is not connected to his own. His parents are nowhere to be found.Konoha Year 63, July: The dream of becoming Hokage fades, as Naruto finds himself detached from the village that once held his heart. The desire to become a Shinigami grows stronger within him, spurred by the hope of discovering the true Soul Society of his world and reuniting with his parents.