Rinko Ozaki is an ordinary high school senior who lives a peaceful life with her father and younger sister and loves her childhood friend, Shinya Mizushima. However, she has had a mysterious birthmark on her left arm since birth. One day, as she grows closer to Shinya, the birthmark begins to heat up, and strange changes start taking place in her body. When her anger reaches its limit, the mark on Rinko’s left arm reacts, revealing that she possesses the extraordinary ability to transform into a wild, uncontrollable beast—a leopard.