Kamen Rider Zi-O: Supplementary Plan is a web-exclusive series released on Toei Tokusatsu Fan Club. It accompanies the airing of the main series' episode the day after it.
In the fall of 2018, a time machine appears before a hero born in the year 2000. The hero has always dreamed of becoming a king. A mysterious girl appears from the time machine, telling the hero “I come from the year 2068, a world without hope where the king of demons reigns supreme.” The girl has come from the future in a desperate effort to change her own time. The girl then gives the hero an ominous warning “You will become Kamen Rider Zi-O, King of Time, the demon destined to rule the world.” Can this really be the hero’s fate? This is the story of a Kamen Rider who would be king, who will fight to save the past, present, and future, encountering the various Heisei Kamen Riders throughout space-time.