Ore to Imouto no Kounai Play ~Imouto wa Dare ni mo Watasanai~ by Magi - Adult Sex Game

The main character has a younger sister, Sanami.
She is cute and the hero is secretly in love with her.
He keeps it a secret, so they have a quiet life.
But everything changes when his friend says he is in love with Sanami.
The hero decides to act so as not to lose his dear sister ..