One Piece: From the Start, Training a Hundredfold, Awakened by Thunder!

[Invincible protagonist + decisive and ruthless + hundredfold cultivation returns + one word: “god”] Transmigrated into Enel on a sky island, he has barely taken his seat as a god when he awakens the [Hundredfold Cultivation Return]. No System missions, no pointless instructions. One day of training for him is equal to a hundred days for anyone else. Six years. Using hazy memories from his previous life, he begins training in the Three Types of Haki, the Six Powers, swordsmanship, hand-to-hand combat, and Devil Fruit abilities... Others train for six years; he effectively trains for six hundred. Six years later... Observation Haki grants Future Sight, Armament Haki reaches the level of flowing blossoms and can be projected outward, and Conqueror's Haki combines with thunder to create a tangible aura of oppression. Devil Fruit Awakening transforms lightning into the [Red Thunder] that annihilates everything. On the day the golden ark, Maxim, is completed, he stands at the bow, gazing down over the White Sea with a cold smile. “Endless Vearth? A god's ambitions should encompass the entire world of pirates.” Then, one day, the Straw Hat Pirates climb up to the sky island, singing as they go. Luffy grins widely. “I'm going to ring the Golden Bell!” Nami is still calculating how many berries all that gold is worth. El Thor descends from the heavens. The day the news reaches the Blue Sea, the Five Elders fall silent, the Four Emperors take notice, and the Fleet Admiral smashes his teacup. The whole world is asking the same question: Just who is that god on the sky island?