Training of Popular Cosplayer's Sister - Final by Almonds and Giant Milk - Adult Sex Game

Overview:
The protagonist, who was living alone with his older sister in the absence of his parents, loved her as a woman.
He spent his days suppressing his warped desire to monopolize her,
but one day, his sister starts cosplaying under the influence of a friend.
One day, she starts cosplaying under the influence of her friend.