It's been eight years since Touma and his allies saved the world from Storious. With the help of Mei Sudo and his new friend Mamiya, Touma cares for a young 11-year-old boy named Riku, who lost his parents during the battles against the Megid. Feeling responsible and wanting to atone for his sins, Touma tries to a father figure to Riku, who continues to go through life without smiling. Meanwhile, Kento has become a book translator and looks forward to getting married to Yuina Tachibana. However, terrible events are unfolding within the members of the Sword of Logos as swordsmen after swordsmen disappear. Rintaro Shindo is dispatched to investigate this and encounters the new Kamen Rider Falchion, Shinjiro Shinozaki, who claims to be his long-forgotten father. While Rintaro is confused by this revelation, the new Falchion attacks both Touma and Kento. Who is Shinjiro Shinozaki and what is the secret behind the terrifying power of Amazing Siren, and how will Touma and the others resolve this one final loose end?