This volume has nothing to do with the first two volumes, and contains a completely new story featuring completely new characters. In fact, even the location is different.
It's like Joshikousei, GIRLS HIGH, except without the slapstick comedy and more... girly angst, as well as some more sweets. Oh, and YURI. This story is more YURI than the first story (volumes 1-2), but if you were to ask if Kanako & Ao are a couple, ... I'm not sure. It's a fine line. ^^;