The Knite contest, which brought forth much silly crossovers and randomness, as well as a Fountain of Memes. If the angst of the real thing ever gets to you, read the entries from yuumei's favourites page.
Author comments, especially on the beta pages
Chapter One Omake. Kai tries to cheer Sen up by offering to buy ice-cream. Sen refuses, saying "don't try to bribe me!" In Chapter Two after Kai has convinced Sen to come to school, they are both eating ice-cream.