Book 2 was written as a continuation to Where the Sky Meets the Ocean (WtSMtO), intended to extend the storyline of the relationship between Eli Ayase and Umi Sonoda that was never told in the series nor the movie. In this story, both protagonists were still sexually inexperienced and they are slowly exploring. Members of µ's were more involved especially Maki and Nico.
This story explored the first-person views and thoughts of the two characters, in their past. It has two parts: Below the Deep Ocean in which was told by Umi and Above the High Sky by Eli. The second chapter of both parts (Welcome to the Family) was set after the end of WtSMtO (also, both parts have the same Welcome to the Family chapter, of the same event but told by respected characters).
The stories are arranged in chronological order, except chapter 2's of each part, with Diamond in the Rough as the conclusion of the story.