Actually, I read a translated interview with Kobayashi or someone related to the production on Ryuki that it was meant to end earlier than they had expected, and that Episode Final (which was maybe why it was called that) was meant to be the original ending to the series. Luckily, somehow they finished.
Don't quote me on this though.
The "movie is the ending" thing I do believe, as I recall that Toei hyped it as such, then of course backpedaled when it became obvious that wouldn't be the case (showing the end midway through doesn't make much sense to begin with, though I can see how it could be done with the right conviction.) I think someone on the staff made the joke that the series was the "Kobayashi ending" while the movie was the "Inoue ending".
But I've never come across anything definitive about the series actually being meant to end early, and a lot of the rumors back in 2002 were that it was doing poorly and was facing outright cancellation (I seem to recall "ending at 39" being tossed out a lot.)
Episode Final does seem a bit like Inoune's stuff. Ryuga's existence felt so damn random to me. "I'm a mirror-man, I'm you, I'm Kamen Rider Ryuga. I want to kill ya all."
^true. I love Ryuga's design for some reason. XD
Shinji had a twin (elder) brother named Shinichi. The two looked exactly the same but had different personalities; Shinji was the same as he is now, Shinichi was more the rough kind. Nevertheless, they got along very well and were really close.
One day some punk attacked Shinji with a knife and Shinichi died protecting him. It turned out, though, that the punk was some guy who'd fought Shinichi before and was after him in the first place, and just got them mixed up.
Everyone says Shinichi had it coming and Shinji grew really depressed and developed a split personality, the other personality being that of his dead brother.
His parents bring him to a psychiatrist and **** and they fix him up by changing the "ji" in his name (it's originally 二 or "two", with Shinichi's "ichi" being "one", indicating how they're the first and second children of the family) so that it's no longer "two", thus supposedly breaking the bond between the brothers.
SIC Hero Saga aren't really a dependable source I think and besides, even if you go with the Hero Saga story, won't it sound better if Shinichi is a mirror monster made by Shinji instead of "I'm a mirror man. AHA"
"Showing the end midway through"? I don't get this.