Dragon Ball God Mu - Chapter 666

Ron finds himself reborn in the world of One Piece, stranded on a remote island in the East Blue. But he's not just any ordinary child—he’s bonded to a mysterious sign-in system that grants him powers with every new location he visits.At his first sign-in, he unlocks the legendary Sun Breathing Technique, along with a boost to his vitality. From Shitmotsuki Village to Skypiea, Enies Lobby to Marineford, Ron travels the world, collecting extraordinary rewards that make him a force to be reckoned with. The Raikiri, one of the 21 Great Grade Swords, Armament Haki, Observation Haki, and more fall into his hands.As Ron steps onto the battlefield of Marineford during the legendary Summit War, the mightiest warriors—Four Emperors and Marine Admirals alike—pause, stunned by his presence. But Ron merely waves them off, “Don’t mind me. I’m just passing through.”Join Ron on his journey across the Grand Line as he signs in at iconic locations, growing stronger with every step. This is not just an adventure—it’s a legend in the making.

[WARNING: MATURE CONTENT]

In the end of the world, the fittest survive.

Come back from rebirth, seize the opportunity, just want to survive in the hopeless end times.

Three months before Mu Nan returned to the apocalypse, he sold all his savings to accumulate supplies, hoarded everything he could hoard like a hamster, and then huddled in his own house and lived a low-key life, carefully waiting for the apocalypse to come step by step…

- Description from Novelupdates