Within a Hollow Heart - Chapter 18: Volume 1, : "Echoes in the Flame"

Outer Sect Disciple Chen Yu, assimilates within his body a fiendgod heart.

The heart, is the backbone of life, the human body’s fatal vital point. And it can be said that Chen Yu’s heart is actually his strongest defense point, and permits him to overtake demonic beasts, or divine beasts unlimited potential.

Henceforth, he steps onto the stage and surges forth on a magnificent scale, in a heart-rending mysterious journey.

Talented as a cloud, an unparalleled supreme talent.

10,000 races glorious, cross boundary battles.

Only my heart, eternal!

- Description from Novelupdates

The strongest Hero in history, Nakamoto Keisuke.

He was summoned to another world in the spring at the age of fifteen years old, and when he successfully defeated The Demon King, he was already thirty-two years old. He had finished his role in another world and returned to Japan, but the reality that had been waiting for him was, “Middle school graduate with seventeen years of blank period” label. He couldn’t find a decent job and had no choice but to spend his days working part-time.

Before such a Nakamoto, a beautiful girl who self-proclaimed had come to return the favor, appeared. “I’m the reward for Hero who had defeated Demon King”, said Angelica, a girl who came from another world that persistently tempted Nakamoto to make her his wife. Together with a high school girl who looks like Elsa, his beloved girl that he lost in another world, Nakamoto with his cheats skills got caught in a harem life.

“You’re the moonlight that lights up the night’s darkness~

On the dawn of a fresh New Year, an ominous figure emerged, shrouded in a guise of an angel but harboring the malevolence of a devil. With a chilling voice, it proclaimed, [Every month, you humans will be thrust into a perilous quest. Your survival hinges on overcoming 20 grueling rounds.]Suddenly, I found myself ensnared in this dangerous survival game, a grotesque merry-go-round where every turn carried the stench of death. Yet, I was not without any defenses. I possessed an unusual power: the power to regress 100 times, a chance to rewrite my fate.I stand on the precipice of my final regression, and I swear, ‘This time, I will conquer it. I will emerge victorious.’I’m no longer the insignificant shuttle that I once was. Today, I shed my former self, the one who had reached the pinnacle of power. Today, I am reborn for the last time as Black Scythe, a rookie player, a novice that once again will be become the Grim Reaper!