Gakushoku no Oba-san ~Kaa-san no Shiru no Aji~

Daisuke is a university student. Though his parents went missing when he was a kid, he enjoys his school life. One day, he becomes friends with two women. One of them is Kumi, his classmate. She is thirty years old and married. The other is Ryoko. She works at a school canteen. It doesn't take long until he and Ryoko fall in love and they finally sleep together.... One day, he tells her about his past. And her face suddenly turns pale and she says, "I can't meet you anymore...." Actually, Ryoko is his own mother....