GVG-850 - Fiancée is a brat? Nanako's early wedding night

It's hard to tell if she's supposed to be young or older. Since they're engaged, there's no guilt, but even if it's a 'shota' theme, it's just an adult playing a kid, right? What's the goal here? Engagements aren't for making babies, and if he keeps knocking her up, the kids are just going to pile up...