Fan no Shoujo ni Cosplay Sasete

The main character is a popular upcoming illustrator with many online fans.  One day, he runs a live booth, and meets one of his most ardent fans, who turns out to be a cute young girl.  The pair exchange contact information and start attending events together.  It's not long before his new girlfriend is drawing in customers and helping his booth's sales by day, with post-event cosplay sex in the evenings.