Don't let that red twin-tailed girl get away!

At some point without anyone noticing, twin-tailed girls suddenly become popular throughout this city. Girls with different hair colors and accessories, but they appear in lonely, unknown corners, characterized by their Unity uniforms and school bags. The missing girlfriend that protagonist Mannenao encounters is among them. Just when he thinks it's merely unexpected, Mannenao becomes involved in a series of thrilling incidents, and must also face crises threatening his close friends around him. Who exactly are these dangerous girls? Enemies? Friends? Girls? Boys? Or something else entirely? How should he continue to interact with his best friend at school? As lovers? As friends? Once he steps even slightly into the abyss, how can he choose?