Spoilers: Ciel is doing something crazy in the background for vol 23 against Ivarage!
Ciel is hard at work recreating "Veldanava" because she has come to the conclusion that Drago Nova would be stronger than Velzard's ultimate attack. If Rimuru must drive away Ivarage, then he'll need to use a swordart stronger than his strongest Void-based attack which Feldway easily parried. And after handily defeating Michael with Void God Azathoth, Ciel believes only an art that can draw out the full potential of Drago Nova's magic: Star King Dragon Arts will be successful against the World Destroying Dragon.
