The Kurtofsky I Ms

The Kurtofsky IMs is an Alternate Universe Fic written by Mags and Tess that is centered on the characters of David Karofsky and Kurt Hummel.

Mostly told in the form of instant messages between the two titular characters, the story, which departs from canon after A Very Glee Christmas, is about the two young men slowly mending fences and starting to gravitate toward each other.

Engaging, funny and with IC characterization (with one small exception), this story can be read here.
This fanfic provides examples of: