MTL - The Roots of Manga - Chapter 25 horrible evil god

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!

It begins on the mountain.

With the glint of a knife, a flash of steel in the hands of a sworn brother. A betrayal.

Stabbed and pushed down the mountain, Zi Chen lied within the red-stained snow, left to die.

This is where it begins; he is given life by lightning,
baptized by thunder.

Those who had once betrayed him should all suffer in his cruel revenge.

- Description from Novelupdates

A boy wakes up with omnitrix as a X-GENE

I exist in the darkness, disappear under the bright light, and will eventually devour the sun and turn into the shadow of all things… Known by people as the indescribable terror of darkness; the king of shadows; the dark day; the existence of the shadow of the world , is still just a somewhat special high school student, facing a weird death game…

- Description from novelbuddy