Some comments on Pixiv seem to suggest that it refers to the Gundam Double X (From After War Gundam X), with the whole Moon thing and whatnot.
If Eirin can shoot the Twin Satellite Cannon, well...
#816 Yagokoro xxAah, Eirin?Yagokoro XX-sama.Well, I don't have any business with you, Eternal Princess. I'm looking for my master.Oh my, Yori'?Yagokoro XX (Double X).Master!!♡Double X...Mon