Adult PC Game: Training of Popular Cosplayer's Sister Final by Almonds and Giant Milk Archive

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.

Training of Popular Cosplayer's Sister Final by Almonds and Giant Milk Gameplay Preview