From what I can recall, it starts out with a middle-aged man seeing a girl sitting on the streets and taking her to his place. Then the rest of the doujin is just them having sex (no real story, just sex scenes) and I think there was a bathroom blowjob scene. Also, the girl had no dialogue, and I believe she was wearing a mask.

Btw, the manga I am thinking of is not "Hirowareta Onnanoko to Oji-san no Hanashi" by Shouji Nigou. (It is similar, but I remember the girl having no dialogue and it wasn't really a wholesome feel like Shouji Nigou's work). I think the title also had a word in it that was in the form of "-hara" referring to a specific type of girl (e.g. menhara), but I'm not confident on it.