This is a spinoff of “Nana & Kaoru”. The story takes place in the third year of high school, after the ending of the manga, but before Black Label (aka Arashi).
Nana to Kaoru ～Koukousei no SM gokko～
Alternative Titles ナナとカオル ～高校生のSMごっこ～, ナナとカオル ～高校生のSMごっこ～ , Nana & Kaoru ～High schoolers' SM play～
Synopsis Nana to Kaoru ～Koukousei no SM gokko～
Author Amazume Ryuta
Artist Amazume Ryuta
Warning, the series titled "Nana to Kaoru ～Koukousei no SM gokko～" may contain violence, blood or sexual content that is not appropriate for minors.