Izayoi Sakamaki, Asuka Kudō and Yō Kasukabe, three children with extraordinary powers, receive a mysterious invitation and are suddenly transported to a world called the Miniature Garden. There, they are greeted by a rabbit-eared girl known as Black Rabbit, who informs them that the world revolves around 'Gift Games', which challenges its players with games of varying danger in exchange for rewards. Black Rabbit first tests the children with a card-based Gift Game, which they manage to win after a tactic by Izayoi. As the group make their way to a village area, Izayoi sneaks off to the edge of the world, where he fights a Gift Game against a water god and manages to beat him. Meanwhile, Asuka and Yō meet a boy named Jin before being approached by someone.
『世界の全てを捨て、我らの箱庭に来られたし』――謎の招待状を受け取った瞬間、逆廻十六夜、 久遠飛鳥、春日部耀は、異世界へと召還されてしまう。そこに現れたウサ耳少女の黒ウサギは、 ３人には神魔の遊戯“ギフトゲーム”に参加する資格と能力があると言うのだが……。
