Throne of the Ghost Emperor (Danny Phantom X Naruto) - Chapter 15

The world that nurtured the civilization which reached the pinnacle of magic was on the verge of destruction.
The last survivor transmigrated to the past, when the magic civilization started growing, as countless mages were still fumbling their ways through the thorny paths of magic knowledge.
He, who came from the end of the magic era, aim to reach the pinnacle of magic.

- Description from Novelupdates

Shao He, heir to a family renowned for medical and poison skills, a top special agent of the 21st century, unexpectedly transmigrated into the body of a pathetic Madam Marquis who had been tortured to death! And on that very night, she was thrown into the Mass Burial Mound!Looking at the newborn in her arms, Shao He resolved to live a splendid life in this foreign world!From then on!She was the Divine Doctor who aided the world!She was the fearsome Poison Queen!She possessed wealth to rival nations!She was also an astonishing scholar!And the Marquis, filled with regret, wished he could kill himself on the spot, “He'er, I was wrong, you...”“Shut up, I am now the Empress!”

Lenny, an orphan from the Sector 41 slums, suddenly finds himself in possession of a rare and unknown affinity. It allows him to upgrade himself, using energy acquired from spirit beasts. But will he gain enough power to defend himself against those with every advantage he has never known?Explore the Western Alliance, where the Four Pillars rule supreme, and all vie for the title of the strongest faction. But when those sworn to protect the people fight amongst themselves, who will save them from the biggest threat they've ever known? And can one young boy, with no family and a handful of friends, survive all that chaos?