Here is my attempt at rewriting the paragraph with the given specifications:
Existence is a bizarre and twisted idea. In one reincarnation, Lee Jain, the reincarnated being, found himself observing the world through the eyes of an ant marching among thousands of his kind. In another life, he gazed at a prehistoric jungle through the eyes of a Jurassic beast. After experiencing countless lives in many forms, Lee Jain was born as a human. However, he was unlike any other human. He wielded the collective power and abilities of all the lives he had lived before.
Lee Jain wondered about the reason behind his seemingly endless cycle of rebirths and his strange power.As he immersed himself in this train of thought,an realization dawned upon him.His existence serves a single purpose:to annihilate humanity.
His purpose became his obsession and fueled his desire for vengeance against mankind. Therefore, Lee Jain honed the powers granted to him over many lifetimes of accumulating experiences. He mastered the abilities of every creature he had ever incarnated as, gaining dominion over almost all life on Earth.
Lee Jain’s hatred blossomed as he witnessed humanity’s crimes against life itself. He vowed to put an end to mankind’s tyrannical rule over the planet. Using the powers under his command, Lee Jain took the first step toward exacting retribution against the human race that had caused so much harm. His attack came without warning, dealing a devastating blow to major cities around the globe as a declaration of humanity’s doom. The annihilation of mankind had begun.
Lee Jain’s vengeance would only end when humans were wiped from the Earth, restoring balance. His existence, eternally tied to the cycle of reincarnation, would continue even after mankind’s end. The eternal spirit within Lee Jain would move on, born into new lives and new forms unconstrained by humanity’s influence. At long last, Lee Jain’s purpose in this life would be fulfilled. Existence would march on, as it always had, without end.