How could he forget that? He was only 6 years old, but he clearly remembered the agony caused by his baby sister's kidnapping. Even though it's now taboo to talk about it at Moon castle, he still remembers everything. He and his father are still looking for traces of his missing baby sister. The agony his family feels is long-lasting.
But so far, their efforts have been in vain. His baby sister seems to have vanished, swallowed by the earth. But they never believed that she was dead, not once. They thought she must be alive somewhere in this empire or even in the mortal world.
"Have you forgotten the reason why she was kidnapped?" Asked Leon calmly with his eyes still pinching.
Xavier froze.
After several years missing, Xavier and his father realized that his missing sister had something to do with her engagement to the Crown Prince, the future Emperor. Someone wanted to boycott the Emperor lineage.