Page 1 - being out in public wearing no underwear was IIRC referred to as "going commando" ... here, it's called "freebirding". The Times Indeed Are A-Changing.
Page 5 - To Satoru-kun: Rinko-chan, your cute, assertive AND horny girlfriend, tells you her switch has flipped, she wants to have sex right there and now, and declares she's okay with a threesome ... in the H-Universe at least, There Can Be Only One thing to do - and that's her (say-no-more, say-no-more).
Ya, I would love to know if that is a translation from J or if that is the translator's colloqualism. Maybe freebirding is slang from where the translator grew up.
"Then we'd be forced to have a threesome"?
She certainly knows her Hentai. Also, I'd like to see that.
Great ending though. Yup, I'd have certainly loved to see her get a scene as well...Too bad.