Osozaki no Hana

For the past several years, 28-year-old virgin Mizuki has been receiving unsolicited dick pics once a month from an unknown man: "Look at my c*ck!"
(This guy gets off to me...?)
Having little experience socializing with anyone, much less the opposite sex, she develops a twisted sort of crush on the mystery sender.
But then one day, the photos stop coming. For the first time, she replies to one: "Are you done sending me your pics?"
He writes back: "Sorry I bothered you all these years, but I met someone, and we're getting married."
Enraged, Mizuki decides to solicit the help of a detective agency to discover the sender's identity.
"Supposing we DO find out who it is, what are you planning to do next?"
"I'm going to look at it."
"What?"
"I'm going to look at his c*ck!"

[Translated from the official site]