Kisei Shokushu Otoko ni Netorare Modaeru Kazoku

Overview

The protagonist is a very usual student. He live with mother and younger sister and she. A certain day, protagonist as usual toward school. The junior of the intention who always is, is not coming.
He did not know. The junior in yesterday, parasitism in "Frightening living thing of the tentacle that attacks the woman" that has fallen from the sky suddenly.
After that the junior, mother of protagonist, younger sister and she is put on the poison fang one after another. With the tentacle that wears the liquid that is the aphrodisiac, mother, younger sister, she... it was swallowed deeply to the whirlpool of pleasure.