Furachi OVA

Kai, a lonely man, discovers by chance through an old telescope that his neighbor Ikenaga masturbates openly every night with her curtains drawn, and he becomes addicted to watching her. When a random encounter brings the two face to face, Ikenaga reveals she was aware of his gaze all along — far from being angry, she admits that after escaping an oppressive, sheltered upbringing, she craved excitement and found his attention thrilling. The two begin an intense, purely physical affair that blurs the lines between voyeurism and mutual desire. As Kai wrestles with guilt and self-loathing, wondering if he is anything more than a convenient outlet for her boredom, Ikenaga keeps pulling him deeper, and he finds himself unable — or unwilling — to walk away.