Ne~pon? x Raipon!

"Where am I?" When the main character wakes up, he finds himself being in a strange world. He doesn't remember anything except for his name. When he is at a loss what to do, a girl suddenly appears in front of him. According to her, this world's been created to celebrate the Navel's four year anniversary and the Lime's one year anniversary, and he's been invited to the world as a guest. Though he doesn't know what's going on, he gradually gets involved in the festival. Ten days in a mysterious world. What will happen to him in the end...? Mahjong-like game with tiles marked with characters of Navel & Lime games instead of standard mahjong tiles.