In the letter were written,
'I can't speak because if I did, Eva might get disturbed. So, I've left everything in this letter. I've already told you about Cyrus, right?
'This is him, my life-bound pet, and his bloodline is as special as Eva. But he's more like a little brother to me and a family like you guys. He's just a child, both physically and mentally. But he can speak, not to mention he's very playful and hates to study…'
In that letter were written some details that Ace missed when he told Alina about Cyrus, for the details about how Eva has appointed Livia to look after Cyrus and his study. She deeply cared about him, and Cyrus also called her big sis and was very respectful towards her.