from "metal-fist X, Mission 01":

Beta walked away from his brother
"give it up X, or shane, your weak, cause you lowered yourself down to human levels" he siad, kicking asides X's removed robotic arm, he grinned as he saw bits of X's ribs fall away from it, "you should give up brother, thats all your good for, thats all that humanity has given you"
"you're...wrong" muttered X slowly tryign to get up, his lungs were burning, felt like he was drowning inside, "rachael...even with all odds against her" he managed to get on his feet "she never gave up" he felt the energy fill his body, "She Never gave up!" he shouted, energy filled his body and felt like it was pouring out of every pore of his being
"what did you say?" beta said, turning round, his cybernetic eyes found it hard to focus on X, it sensed the optical presence of X, but the physical presence was on the same levels of a nuclear explosion. beta heard about something like this, Psyonic energy, sonic energy molded into a weapon by overwhelming psychic energy, it was in all the old notes, they said that project x, was capable of using it, but he never thought that his brother, a raised by humanity, could use such a thing, then he saw something amazing, X's left arm wsa growing, regenerating, "so much energy" he muttered "its accually regenerating a body part thats been dead for nearly a year" he stepped back, as X's eyes filled with power.
"This is the power of Humanity, this is the power of My humanity!" he said, the shock waves from his words alone sent Beta back a few feet
"i-impossible" growled Beta, his body was made to withstand any weapon known to man, but X's voice, it sent all his senses into critical-readings, and only one thing was clear in his mind "i could die?!"