The unknown

Since the Youth Day phenomenon occured at 11 AM, Dan, 43, was hornier than ever, waiting impatiently in his home.
Waiting who ?
"Her"
He didn't know her name. But three months ago, during a Youth Day, "she" knocked at her house. A gorgeous woman like he never saw before. She didn't tell him who she was but she seemed vaguely familiar for Dan.
She just wanted to have sex with him.  And she had. Dan had the best sex he had into his entire life. But after she had what she wanted, the unknown disappeared... just to come back the next Youth Day.
And she was at the rendez-vous this Youth Day again. Dan tried to obtained some info from her but she wasn't here to talk.
Dan didn't know what to do as the mystery seems to make their relationship so exciting. But at the same time, he was so curious !