What is a "gal wife"? In Ar Tonelico Qoga: Knell of Ar Ceil, when in Tyria's route (well, more being locked into her ends than a separate route), she expresses her desire to be Aoto's gal wife.

Now she's not the first to express wanting to be with Aoto, as Saki numerous times expresses how she would want to marry Aoto in her Cosmosphere. However, in their True endings....


   Saki just has a wedding, wanting a private ceremony, while with Tyria, she's already married Aoto and is wearing something almost like a naked apron (she is wearing panties but I think that's it)


So when Tyria says she wants to be Aoto's gal wife, what does she mean exactly? How is a gal wife different from a normal wife?
The literal translation for that is something along the lines of "young wife", as the original script uses "幼妻" instead of the "gal-wife" expression NISA made up. So she's pretty much boasting that she's going to be Aoto's wife despite being so young-looking.