From the start, Touma would have already been an experienced swordsman and had all of his missing memories involving Luna. Touma, a lone traveler akin to Soji Tendo, would have had to embark on a 'road trip' and encounter each of the other swordsman while deepening his bonds with them before their final battle against Storious. As revealed in the 284th issue of Figure-Oh Magazine, the original proposed drafts had a vastly different story, where the members of the Sword of Logos were originally at odds with one another, with each Swordsman located in different areas around the world.
The concept of battle royales between multiple Riders has been done in the past, like Kamen Rider Ryuki. Twelve Kamen Riders of varying alignments have appeared throughout the series.
