Naruto System in One Piece - Chapter 512: Gaara vs. Deidara

Kaden awakens once again at the dawn of Earth’s cataclysmic “System” invasion, armed with haunting memories of his previous nightmare life. Desperate to overturn his grim fate, he sets his sights on a special druid class—only to unlock a legendary hidden class!A druid who had to devour to become stronger!With every enemy he devours, the madness increases. The nature twists and contorts in his presence. Plague spreads where he goes. The cursed forests become his grove.Would the fallen druid be able to face the twisted alchemist who once enslaved the entire planet? Can Kaden master this cursed power to save humanity—or will it consume him, turning him into the very evil he seeks to destroy?

After breaking up with his girlfriend, he accidentally acquired a genius system and rose from there against the heavens, becoming invincible..

- Description from Novelupdates

Buried alive. Forgotten by the world. Cursed to refine death itself.Rin Xie clawed his way out of his own grave with nothing but broken nails, shattered bones, and a core pulsing with rot. In a world where the heavens punish the wicked with celestial fire, where death cultivators are hunted like beasts, Rin awakens with a forbidden path—one that feeds on pain, suffering, and the ashes of the dead.He cannot heal. He cannot forget. But every wound, every betrayal, every death he witnesses becomes fuel for his ascension.Under a crimson eclipse, he walks through battlefields where spirits still scream. In deserts of bone, he consumes lotus flowers blooming from despair. He learns techniques the heavens sealed away in fear—Soul Wither Pulse, Requiem Bloom, Grief Reclamation.But the deeper he dives into death, the less human he becomes.He no longer cries for the fallen.He no longer prays for peace.He begins to wonder—what kind of death should he become?In a world where power devours morality, Rin Xie will either become the end of all things...Or something worse.

Eren Idril died as an old, decrepit, and piss-poor adventurer by the maws of a D-Rank monster. He had a lot of unfulfilled dreams and desires that couldn't see the light of the day after the light in his own eyes died down.

But fortunately for him and unfortunately for the world, that wasn't his end. Eren was somehow dived back in time when he was a mere teen, attending Lionheart Academy for adventurers.

When life gives him a second chance, Eren decides to exploit it to its fullest. Experience his vile deeds as he partakes in them without feeling the slightest bit of hesitation.