The Memory Lake was discovered by the late Emperor Idelfonso during his reign. Upon bonding with its consciousness, he discovered that the being chooses its own master.
Knowing this, Emperor Idelfonso tried if Emperor Valentin could also be recognized as the next master, fortunately, the Memory Lake recognized Emperor Valentin as it's next master.
Soon, when Emperor Idelfonso died, Emperor Valentin had all his sons submit a drop of blood for him to offer to the Memory Lake. Out of the three princes, only Leon's blood was absorbed by the memory lake and was recognized as its next master.
When Emperor Valentin asked the spirit of the lake, why he chose the weakest son out of three to be its master, the lake simply said, "He has the capability to maximize my abilities the most."