Itazura Katei Kyoushi ~Misshitsu no Waisetsu Shidou~ by REAL - Adult Sex Game

Hero Sakamoto Koji, aspiring to study at the Faculty of Education to become a teacher, while working as a part-time home teacher for Yuki, the eldest daughter in the family.
But his student is a rebel, and therefore learning English is difficult. One day he receives an envelope. There was one DVD in the sleeve. Cautiously checking the contents of the disk on the computer, it turns on the video.

The shooting location is well known to him. Yes, this is Yuki's room.
On the day of training, the teacher checks the room from the same angle that the video was filmed. And finds a well-hidden prying camera.
Who posted it? And for what purpose?