Rean used his Light Element to reduce the speed which Uruavis deteriorated but didn't urge Yuan to hurry up. Yuan had to get a full grasp of the method before trying it out, so giving him the necessary time was a must.
Yuan used his own bloodline to practice it. He would draw his blood out and hold it with his Spiritual Sense. Then, he would use the method to absorb it back into his body before repeating the process. That was the easiest way to do it since there wouldn't be rejection issues.
Finally, two hours and something later, Yuan nodded, feeling like he was ready. "Rean, this is it. You made this complicated technique very easy to understand in the instructions. I don't think I can get any better now."
Rean smiled at him. "That's good then. Let's give it a try."