Negi Nogami, also known as Kamen Rider Nega Den-O, is a villainous counterpart to the main protagonist in the series Kamen Rider Den-O. Nega Den-O is an evil version of Kamen Rider Den-O, wielding the Nega Den-O Belt and the Nega DenGasher. He appears in the film 'Kamen Rider Den-O & Kiva: Climax Deka,' where he opposes Ryotaro Nogami and his allies. His role is to create chaos and challenge the Den-O team, showcasing the darker side of the Rider system.