I like the fact that even with the secret to win being pretty easy, in the end it's truly a game devised by a devil.
A game where all hope is lost in the end after initially rousing it with sweet promise.
To be honest, i'm somehow wishing that in the end, the MC will win by some other method, making him still has the right to the wish. One method i could think of is somehow tricking the demon to play rock.
Tho, there is a chance that instead the MC will use his wish for her sister, basically trading his soul.