Rei proved it that he knew about Serafim more than any living being in this realm. Even Lu was not really aware of Na's true power. Rei knew a lot and his knowledge himself was a threat for them.
"Gnomes represent the earth, Undines represent the water, Salamander represent fire and Sylphs represent the air. The air magic stone was the last she created because it took a lot of her to get it done and while you can find a lot more magic stones in this realm, you can only have one air magic stone. She perfected the last magic stone with her last breath, that's why the Sylph is very powerful."
"How can you summon a Sylph?" Iris saw the spirit and even though it was not as strong as the one she summoned, it surely stronger than the one Abby summoned.
