Netokano - 1

The main character Mizuki Suzumori since childhood is in love with the neighboring guy Sota by the Cossacks. Everything is like love, promises to enter the future at the same university. To receive the cherished recommendation, Mizuki visits the section of light athletics and she needs to leave for the summer for a training camp. It would be nothing, but soon a strange disk comes "for Cossacks " from an unknown sender.
The hero includes a disk and sees his beloved in the hands of an unfamiliar man. But who is this man and what our Mizuki does with him already from the video.