I totally agree with the above, that was superbly well made, perhaps even one of the most "fitting" Den-O fan-openings/animations I've seen since they started making them back when the show was still airing. The music, context, and animation all fit pretty well in relation to the context of the series, though there is perhaps a bit too much usage of Ura-Ryotarou, and the calendar-system bit could be modified to more greatly take advantage of the time-travel aspect (Why did they include that "train station schedule" bit with the various shifting dates in the early promos and then never use them in the show or future promos afterwards?).
In fact, that was one angle of Den-O I'm surprised they never really examined. Back when things were being announced it seemed that the Imagin were sort of representative of their host and/or a facet of their personality/wishes. There were even rumors that Ryuutaros was representive/made from Ryoutaro's own fears, and he had to face them in order to gain control of "Gun Form." They never really took that angle, and instead just made them more simplistic characters with themed aspects (based soley on well-known bits from their "Source Material Story/Fable/Aesop/Legend") and then just "individual beings" of their own, just "tied" to Ryoutaro and mainly existing for combat or comedic purposes.
They could have had Ryotarou's Imagin being indicative of various parts of himself, sort of examining questions of "Who am I really?", "Who was I?", "Who could I become?" (inhibitions, inner hopes, wishes, desires, needs vs. wants, envy, fear, courage, "self-reflection", and so on) and tieing that into the time-travel and memories aspects. Even making actual reference to the story's and their meanings in the plot (or at least noting them beyond the first episode) might have helped put a more unique spin on things instead of just using them as a chart for "MotD" ideas, and leaving all the "in-jokes/references" in obscure expanded materials.