Ore ga Mita Koto no Nai Kanojo

A couple in love, thinking about marriage, have a tough decision ahead of them. They might have to move in with Tomoya's father. However that isn't even the start of the problem, upon showing up at his father's house, Kanako realizes that not only does she know his father... but she has slept with him... multiple times.

Note: A live-action AV adaptation (URE-051) was released on September 7th, 2019.