With what is she having sex ?

Most likely a vibrator, you can make out a pink thing with a cord near her hand.

...since when are vaginas that deep?

well, they are Youkai vagina!
Though, that one could also be a divine vagina. If we go by the theory of Shinki making Alice instead of taking her from the human world.

remilia said:
...since when are vaginas that deep?

Since hentai stopped giving a rat's ass about anatomical correctiveness.

so it's in proportion with her eyes?

MC_Nobody said:
so it's in proportion with her eyes?

... That made a lot more sense than it should, actually ...