You kids don't understand the immense potential of the skill "perpetual motion". In physics, perpetual motion is basically an object that keeps moving without ever stopping, even when force is applied to stop it, it will resume moving after a while. Do you guys remember those giant wind turbines used back in the day to generate energy via wind through the wind moving the turbines and generating energy, imagine that but even without wind, it still moves continuously, forever without ever stopping, that's unlimited energy forever.
A skill that works in that way means whether he actively absorbs demonic energy or not, he will automatically be generating demonic energy always, unlimited, forever. That means even if he laze around all day without doing anything, he will still be getting stronger. That is the greatest of skills ever.
A skill that works in that way means whether he actively absorbs demonic energy or not, he will automatically be generating demonic energy always, unlimited, forever. That means even if he laze around all day without doing anything, he will still be getting stronger. That is the greatest of skills ever.