Kamen Rider Decade/Headscratchers

What happens to the coffee shops that the photography studio keeps displacing? Where do they go? And if there are people in them, where do they go?

They go to the world that the photography studio started in.
Or they were empty buildings. Or an empty lot. Or they just don't exist for a little while.

Why doesn't Yusuke actually help Tsukasa more? He's a Rider, too! In Ryuki World he could've fought for Natsumi as well, and in Blade World he could've helped hunt down Undead.

It's quite likely that he's unable to enter mirrors in the Ryuki World. As for his lack of help in the Blade World, your guess is as good as mine.
- He tried to offer his help in the Blade world, but was misunderstood by the BOARD chairman as wanting their help. To which he got told, "if you want us to help you, you need to pay us." As for why he doesn't transform into Kuuga more, it's probably so we don't get treating to one of the more popular Riders getting the holy crap kicked out of him every week.
  - Additionally, regarding Ryuki's world, he was focused on helping Shinji find the truth in the real world. Even if he transformed and went into Mirror World, he isn't exactly a lawyer and probably couldn't do much to help on that front.
    - Also, since he wasn't chosen to be a Rider it would have probably caused a mistrial.
    - I'll buy it, but with bile in my throat. Now what about Faiz?
    - He can't go into Mirror World. Decade's belt lets him do it, but Kuuga has no ability to. Also, the Undead sucker punched him when he tried to transform in Blade World.
  - Faiz protecting his own home. Nuff' said
  - I get the feeling that the effects budget on this show is pushing the breaking point as is. Since Kamen Rider doesn't use Stock Footage it means one less henshin that they have to pay for.
- Then he finally transforms in Den-O World only to have Momotaros shove a sword up his ass and use him as a morning star. What's up with that?
  - Rule of Funny. It's Den-O's world after all.
    - And Kaito stole the real card, originally it was meant to turn Den-O to the Denliner and run Decade through and give him Climax Form armor, said armor splits into all 4 taros beats the crap out of the foe as seen in Ganbaride
- Then he finally gets to transform and do something useful in the Shinkenger world.
  - And RX's world, and Amazon's world... I think the writer began to realize that he has Kuuga to use instead of just some Butt Monkey.
    - This is probably spot on. Notice how all the episodes he transforms in (after the Agito arc) are primarily written by the same guy.
- The Kuuga question is the most commonly asked and the most obvious. SO KUUGA DOESN'T STEAL ANY SPOTLIGHT. If Kuuga showed up in every other world, you would see that world's Rider a little less. And it's only a little, I know, but with Decade and Diend pretty much shoving the world's Rider into the background as is...

What did Daiki do with the belts he stole in Faiz's world?

I think it was just to show Daiki's Phantom Thiefy-ness, because after Faiz's world, he either does not get the tresure, gives it to someone else/the original owner, gets a substitute tresure, or just gives up all together.
- could just be that he stole some stuff off-screen, but kept it secret

What did Tsukasa and the others do with their Kivala imposters in Kabuto's world?

Lunch.

Why didn't Natsumi (or anyone) show shock that Grandpa and Kivala were alright after the studio got vandalised during the Amazon World Arc?

Other things on their mind.

Where did all of the laser bolts come from in the final episode?

In the fight at the end of the finale the 10 Heisei Riders surround Decade and begin beating him up. As this happens laser bolts start flying on and off the screen in different directions and not a single one (well maybe just one) flies out from one of the Riders' weapons. Did Kaito use an Attack Ride card to fire multi-coloured laser bolts?

Clearly, the answer is that it happens in Hakurei no Sekai.
Or maybe they're fired by the second-string Riders from the various series, who want to help but are smart enough to not even be in the same shot as Tsukasa "Destroyer of Worlds" Kadoya.
It's more of a Shout-Out to the training scene from Black RX.

Why doesn't Kamen Rider Kivala function at all like the other Kiva riders?

She isn't a fangire, Kivala doesn't bite her to transform, her henshin process doesn't involve the whole "turn to glass and shatter" process that all the other Kiva riders have, and she doesn't use fuestles for her finishing move.

Seriously, what gives?

Maybe Kivala's power changed when she passed through with the others.
Another possibly is, judging by Kivala's size, she may be a younger member of the species, and so may function differently.
Because she has no Fuestles.

About Diend...

This has been bugging me for awhile, but why doesn't Diend have something to ride on like the other riders? He is a Kamen Rider, he needs to ride on something!

Addressed here.
- Well, Shin Kamen Rider Prologue and Hibiki aren't exactly known for riding something (while transformed at least), so why should Diend?
Not all Kamen Riders have motorcycles. Quite often it's only the main one, especially if there's gonna be three or four or more Kamen Riders in a show. Partly because the show's budget can't always stand making that many custom motorcycles, partly because it doesn't necessarily fit the characters of all of them. Diend is sort of sneaky and likes his stealthy slinking in and out of the shadows, trying to do that on a motorcycle wouldn't work too well.

Here's a big one that bugs the hell out of me. What happened to the movie that was promised at the end of Episode 31? Final Chapter is NOT that movie.

There was a last minute change. I don't remember what happened, but the movie became an impossible, so they changed the last episode, starting at the point where Kuuga was revived as Ultimate Kuuga. The scene became the Rider war scene from Ep. 1 instead.
No. Final Chapter IS that movie. Somehow Tsukasa manage to escape the fight and start his journey as the destroyer of the world. Of course, some scene has changed, such as no Natsumi with a gun, or the scene where Tsukasa is washed up on a beach. The fight between two Tsukasas are only appear in his mind in Director's Cut, telling him whether to follow his destiny or not

Was Tsukasa chosen as the Great Leader of Shocker, or did he form it himself? They never addressed it, did they?

Yes

Where does the Dai-Shocker movie fit into the series' continuity?

Tsukasa's original goal was to find his way back to his own homeworld, and the movie is when he ends up there, where he's revealed as the leader of Dai-Shocker. But then he leaves for the next world at the end?

Well, personally I feel that both movies are after the end of the series, but that only holds up if you accept the broadcasted episodes 30 and 31 as canon.
- It seems to take place after Black RX's world. Look at the end of #27 as Eijiro puts up a picture. It's the same one Tsukasa and the others look at in the movie.

About Den-O

Now, supposedly, only singularity points can become Den-O. Now, Tsukasa could potentially count, since he's some sort of dimensional anomaly. But why could Yusuke and Natsuki use the Den-O belt when possessed by the Imagin?

Possibly because they're not of the Den-O World, and therefore may be exempt from the rules of its timeline.
Or that by traveling time and dimensions, they've become something close enough to a singularity point that the belt works.

I've just started this series. But something is nagging at me from the very start...

How the hell did Wataru, of all people, become the representative of the original Riders?

He's the most recent?
They probably just recorded it right before the finale of Kiva

How the hell does Diend see?!

How?!

It's really hard to see, but there are eyes on the helmet. They're visible if you look close when he Henshins [before the cards slot into place] and when viewed from straight ahead. It's one of those things that is best shown with the toys; but they are there.
The Playstation 2 he's wearing renders everything in 3D graphics for him, though some of the polygons have slightly jagged edges.