The Dark King - Chapter 5

Xia Yan passed through to the world of Bleach and became an eleven-year-old boy. He was rescued by Renji and Rukia in the Seireitei, and he was studying at Shin’ō Academy, and he was a student of the same class.
He is a top student of the Shin’ō Academy, and he is vying for strength by various teams. In the end, he has entered the first team of secret mobile maneuvers.
He will use punishment to kill every person who tries to threaten the martyrdom and protect his loved one.

- Description from Novelupdates

Ye Chen, once the unrivaled immortal standing at the pinnacle of the cultivation world, fell at the final hurdle—his last heavenly tribulation. Struck down by the wrath of the heavens, his body was destroyed, his cultivation shattered. Yet, instead of vanishing into oblivion, his soul defied fate itself.When he opened his eyes again, he was no longer in the vast cultivation realms but in the familiar yet distant world of modern Earth—inside the body of his younger self during his high school days. Armed with the knowledge and power of an immortal, he would rise once more, overturn destiny, and reclaim his supremacy in this new world.

I am the sword.
Killing a man amidst a thousand miles, no one dares take ten steps.
Killing a man amidst a thousand miles, no one can take ten steps.
Killing a man amidst a thousand miles, ten steps? Not possible!
I am the sword, the sword is me,
On the path towards heaven, each shall wield their own.

Born to a mother on death row and subsequently raised in the prison, Gu Tianyou did not have what most people would consider a ‘normal’ childhood. Instead of the usual math and history one might learn at a public school, he had criminals for tutors. He received regular lessons from notorious serial killer, Dr. Miao, and earned protection from the respected Master Long.

With such a unique background, Gu Tianyou graduated from the Police Academy with little difficulty, and was assigned as an undercover cop. But will the skills he learned from a lifetime of being cared for by criminals be enough to help him take criminals down?