Visitor from the Abyss

A man weary of life meticulously and elaborately planned his own splendid demise.
But after death, because of his profound sins, he was imprisoned in a jail that held the most wicked.
At the same time, the man formed an unspeakable connection with a malevolent deity from the deepest abyss. Was this a blessing? Or a curse?
One day, the prison warden opened the cell door: "You are free, but the cost is, you will participate in the most chaotic and bloody infinite competition..."

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The protagonist isn't a villain, but simply has a moral compass that differs from the norm.