This collection of short stories links the stories and characters in Please, Hydra, Lovers and Souls and Rules.
In (1,2) Kiss and Kiss After, Ryuu has arrived in Tokyo and is about to become a third year high school student, however it's time to change schools again. Before he leaves, his friend Sekai confesses to him. Follows Chapter 5 of Please (A Bird at Sea, a Door in the Sky).
(3) Skies (Hydra chapter 0.5): Our first glimpse of Hikaru (from Rules) in high school, after Ryuu's arrived in Tokyo, and has transferred to his and Hitomi's school. The connection between Hikaru Taira and Yuuji Itou. Continues in Hydra.
(4) Heavenly (comes between Hydra Ch. 6 and 7) More with Hikaru, Ryuu, and Hitomi. Hikaru reflects on his current situation with Hitomi while remembering their first meeting. (Liquid Passion)
(5) Real Thing: Hikaru centered, it links Hydra with Lovers and Souls.
(6) Fragile: Tooru centered, it links Lovers and Souls with Rules. Also involves Shige and Ryoichi (from Please).
(See Rules Synopsis for more information on Rules series timeline. See also Hydra.)