The pinnacle of yuri comics, created by the leading figure in the genre, is finally here with the long-awaited fourth volume. Aiko, who has realized her uncontrollable feelings for Mari, ends up sharing a kiss that is different from what "friends" would share. While Aiko's feelings for Mari continue to grow stronger, Mari, on the other hand, does not perceive the kiss as anything more than a "friendship," leading to a repeated misunderstanding between the two. And then, the fateful school trip arrives...