Please recommend a sci-fi fantasy novel from more than ten years ago. The theme is about the invasion of alien creatures. It describes the resistance of humans, including martial artists like mages and ordinary warrior martial artists.

Every martial artist who wanted to become a martial artist needed to inherit a crystal left behind by a dead martial artist, plus a huge amount of energy to transform into a martial artist. The protagonist began to transform before a battle, and the senior who led him to participate in the surrounding battles died. The protagonist relied on the energy of an alien creature that died around him to successfully transform. He also had the ability to bulge his muscles in battle despite looking thin and weak. He became very strong. It seemed that the reason why he could kill alien creatures at will was because the dead creature had this ability. He was still a primary school student more than ten years ago when he saw it. It was a pity that he did not see it later. Please tell me the name of the novel. p-p