The TV series is divided up into three scenarios, "dream" (ep. 1-7), "summer" (ep. 8-9), and "air" (ep. 10-12).

The game/story in general is divided into three sections as well. The first section is called "dream" and ends when Misuzu's first scenario finishes. Then it moves to the second section "summer" and the last section, "air." Although, the first scenario, "dream," has all three girls, the last two are just Misuzu and Yukito.

The Air game is very different from the set-up of Kanon. In Air, the player cannot beat the game unless they got the happy endings for Kano and Minagi, which unlocks Misuzu's ending and the last two sections of the game. The game is different from most games because there is actually a girl he's supposed to end up with, instead of a choice.

Thank you Mariko-chan for the information! ^^