Evolve to Devour

Everyone in the beastmaster world takes Ryan Summers for what he appears to be, an F-rank Muckhide Serpent, the lowest thing there is. He is a man who woke up in that body after crossing over. The girl the academy calls its beauty turns him down, the rest of them make a joke of him, and it goes far enough that he ends up close to dead. That is when the Devouring Evolution System opens in him. He eats a Shade Wolf first. The serpent thickens into a python, and the line runs on from there toward a Creation Dragon that can shake the world. The Beast Horde comes over the whole planet around then, with invaders out of another world behind it. Ryan takes the human side of the fight and goes on eating what he kills, gods among them, to push the evolution further.