Kain, who was a game commentary YouTuber in his previous life, realizes that he has been reborn into the world of a dating simulation game he was playing right before he died. In this game, Kain is a target character for the 'Cool Senpai Route,' and his sister is none other than the villainess! To ensure his sister's happiness in this world, Kain strives to prevent her from becoming the villainess.