Nana is a normal teenage girl in her last year of high school getting ready for college admissions tests during her summer vacation, with the exception of one thing: She takes "breathers" with her childhood friend, Kaoru. An encounter with Tachibana, a worker she knows at an S&M shop, brings Nana further into the S&M world as she learns what it means to be master and slave.

This “Arashi” series begins 8 months in the future of the Young Animal version, with Nana and Kaoru in the summer of their final year of high school.

This series uses a different support cast & different location setting than the original serialization, and as such it doesn't really spoil anything from the main series.

(Source: MangaHelpers)