Shin Zangetsu, also known as Kamen Rider Jam, is an antagonist in the series 'Kamen Rider Gaim.' He is a manifestation of the dark side of Takatora Kureshima, created from the Helheim fruit’s influence. As Kamen Rider Jam, he possesses immense power and is a formidable opponent to the main Riders. His menacing presence and twisted sense of justice make him a unique and memorable adversary, pushing the protagonists to overcome their own doubts and fears.