When a brother and sister unexpectedly cross paths at a social mixer, a provocative game of "King's Game" pushes their boundaries to the limit. As the dares escalate from suggestive to explicit, the pair gives in to their hidden desires, leading to a shocking confession and the start of a forbidden relationship.
After discovering a mysterious hole in the wall, the protagonist realizes his sister, Sayaka, has been using it to secretly invite his advances. The two enter into a taboo relationship where Sayaka embraces her role as her brother's personal "cock sleeve," leading to a cycle of daily pleasure and a confession of their mutual, forbidden love.