A "what if" alternative version of the original story, on which the cast gets acquainted in a different manner.
The basic premise is that Kodaka, a rude looking and easily misunderstood transfer student catches a glimpse from a conversation between Sena (the most popular girl on school) and "her friend" Renka (a character from a visual novel); after a short discussion followed, Sena decides to give it a try and make some friends with Kodaka's help.
This is a tweak from the original premise, on which Kodaka catches Yozora speaking to her "air friend", and is Yozora the one who decides to start practicing how to make friends with Kodaka's help.

(Source: MangaHelpers)