Super Kamen Rider Den-O & Decade Neo Generations: The Onigashima Battleship (2009)

In 1980s, Ryotaro and the company save a shy boy Yu when he is attacked by demons that came from the past. The demons want to change the history using a supernatural stone what is a keepsake from Yu's mother. Yuto already disappeared in front of Deneb in the future world under that influence. Yu decides that he joins them to fight against the demons.