So, the story sums up to this. Local japanese girl tricks foreign blondie to cultural exchange at her home town. Apparently the japanese girl's home town has a declining female population, and ontop of that, they practice old customs of red light district or females is a shared resource which is property of the town (apparently the main attraction + income is red light district, like the entire town IS the district), and doesn't belong to a single man kind of aspect. So the plan was to get "extra" girls to boost the prostitutes in this town to even out the male female ratio (the translators literally say prostitutes).
That sums up pretty much the entire story, up until the last page. ZA WARUDO. Whassup! Guess what? The blonde chick knew about the japanese girl's plan all along, and it was ALL PART OF THE KEIKAKU(plan) to earn her trust to slip into the town to kill the old guy, she's an assassin.