The limited edition of vol 6 includes a 18-page booklet depicting a day in the life of Yuzu and Mei. Is just a series of pinups with no dialogue but is pretty cute. The extra is a small scene between Sayaka and Miyabi.
And lastly, Sabu's afterword has her (according to the spanish translation at least) very excited about new experiences that she has gone through that have "stirred new feelings on her" that she will use to continue bringing happiness to Yuzu and Mei. So there will be citrus for a while.