Yuuwaku no Toiki

Tetsuya is a 4th grade college student who takes up a part-time job to tutor one of the daughters of a famous novelist in his mansion. But for a salary of 1 million yen per month he also agrees to serve as bodyguard to novelist's wife Ayako whose life is endangered by an unknown person.

Mansion is full of weird characters like novelist himself with a double personality, lover of one of the daughters who attempts to rape juvenile members of the family and even some of the daughters who succumb to lust in broad daylight. It's a very mediocre game full of spontaneous H events, but the resolution and epilogue are quite good as all the mysteries get revealed. It's quite a good concept that was utilized in JAST games a lot afterwards.