My Final Boss is a High Schooler

For ten thousand years, I, the Unbroken Fist Emperor, Bai Kenji, stood as the ultimate guardian of the Azure Cloud Realm. My fists could pulverize stars, my will could bend reality. After finally vanquishing my arch-nemesis, the Shadow Demon Emperor, our cataclysmic final blow shattered the veil between worlds. Now, I've woken up in the frail, pimply body of a boy named 'Kenji Bai' in a world called 'Earth,' a realm of deafening metal chariots and glowing poison rectangles. My only goal is a peaceful retirement, but my plans are ruined when I discover two things: one, my powerless new 'little sister' is a target for shadowy forces, and two, my arch-nemesis has also been reborn here... as Jin Akari, the school's beloved, overachieving student council president. He's thriving, while I'm stuck dealing with pop quizzes and gym class. I must reclaim my power from deep within this planet's core, protect my new family, and finally crush my rival, but how can an Unbroken Fist Emperor win a fight when his biggest challenge is asking his enemy for a hall pass?