The Kaiju King

As a result of Kawasaki Ken's anguished soul inadvertently fusing with The Ruby, a primordial power of unparalleled antiquity, he gains the extraordinary ability to transform into one of the legendary monsters known as "Kaijus". But no power goes unpunished as a mysterious requiem begins to echo across his mind, tormenting his heart and driving the need to find the answers to his misery. Somewhere along the way, he finds uncanny friendships, allies, and much more. Traveling together, they explore the universe, pursuing their individual dreams and unraveling the mystery of these ancient powers.

(Also submited to royalroad under the name reaperking19)