(No System in this book. Multiple heroines, but no harem protagonist.)
A rural schoolteacher’s soul transmigrates into the world of One Piece, only to discover that he has the Zafkiel Astral Dress within him. Using its power, he joins the Marines, defeats the Seven Warlords, takes down the Four Emperors, and eventually leads the Marines in an assault on Mary Geoise. But on the final island, Laugh Tale, he uncovers a shocking secret. See how Reno uses an unconventional power to surpass everyone and become the strongest in the world.
My evaluation is that this is too idealistic. And this time, the main control of the gang is to control how big it is, because the protagonist can practice three kinds of skills at the same time. Don't say that the protagonist has such a plug-in. Then Garp and his geniuses are all geniuses among geniuses. Why don't they practice together? It takes a long time to study just the overlord color talent and the weapon color. The protagonist in My Wuyan is not a special race, and there is no system. There is only one ability in the comics