This doujin makes literally no sense. It must have some context because Kasuga just wouldn't go into a random town and put on a sex show nude, let alone let random fucks fuck her, let alone masturbate in public. Wouldn't put her being nude past her though, girl seems comfortable with her body. Needs a translation for SURE. Someone get on that, please!
I was thinking it was out of character too, but it looks like a standard exhibitionism story to me. Character gets nude --> Realizes she likes how it feels --> Excitement of possibly being seen turns her on --> Gets seen and decides to screw them cause she's horny Rin wouldn't ride around naked either, but it's a doujin, and this is how our favorite characters act here.