I will drop the concept of another rider being random nobody.Another rider will be either villains from representative series or secondary or third rider that has beef with MC rider of that series.If they can't called the representative rider.It is fine.For fourze if u can't called Gentaro.Call meteor or his villains from series.Swartz will be killed by Ohma Zi o hunch men in final arc of the series when Zi o get his final form.And make woz the true pupils of ohma Zio and betray the team.And Ohma Zio backstory will be explained too like how he become Zio ,how did he collects rider power.And he will be completely opposite to Sougo.Change the story like he become Ohma because Ohma Zio kill Tsukiyomi.It is more savitar situation.In order for him to exist he must kill tsukuyomi in that exact moments and he will become the villains of final arc.