A finished fill for this prompt: http://sherlockbbc-fic.livejournal.com/10852.html?thread=54496356#t54496356 which said
"John is secretly a unicorn.
Sherlock is a virgin.
John is understandably possessive/protective."
De Veritate Unicornis Modernus (On the Truth of the Modern Unicorn) on AO3 (http://archiveofourown.org/works/722780/chapters/1340661) and on fanfiction.net (http://www.fanfiction.net/s/7346964/1/De-Veritate-Unicornis-Modernus)
no subject
"John is secretly a unicorn.
Sherlock is a virgin.
John is understandably possessive/protective."
De Veritate Unicornis Modernus (On the Truth of the Modern Unicorn) on AO3 (http://archiveofourown.org/works/722780/chapters/1340661) and on fanfiction.net (http://www.fanfiction.net/s/7346964/1/De-Veritate-Unicornis-Modernus)