User blog comment:Jopjopjop/SlashDog/@comment-16281343-20150321011728/@comment-16281343-20150321122316

Oz is the name of the place they gave to the dimension in the Dimensional Gap they're living in. Thuz, Wizards of Oz.

It is certainly a reference to the novel as the name of the Utsusemi that they gave to Sae is Cowardly Leo.