Scent of Seductive Flesh Final by Elf - Adult Sex Game

Takuya is a university student in his final year.
He wants to earn some money so that he can go on a graduation trip with his girlfriend, Yuki.
He starts working as a live-in home tutor for Otoha Misawa at the Misawas' house.
One day, he finds a hole in the wall in his room. He looks into it and sees Kaori, Otoha's mother, doing her hair.
It seems he can peek into Otoha's parents' bedroom through this hole.
Who made this hole? And what is it for?