POKEMON RIDDLE #9

I am the shadow of a secret, born in a lab from a fragment of a myth. I was crafted to be the ultimate weapon, yet I am defined by the soul I chose for myself, rather than the one I was given.

I am one of the very few who can reach two separate peaks of transcendence—one that sharpens my mind into a psychic blade, and another that swells my muscles with a fighter’s instinct. My heart is said to be the most savage among all my kin, yet I spent my life in a cave of silence, waiting for a challenger whose heart could match my own.

I am the only one who can claim that my "birth" was actually a "creation."

Who am I?