Natsumikan is probably Decade's most powerful enemy.
To be honest, I'm getting disappointed with Decade.
1. In the 1st episode, Seto Koji appeared, reprising his role as Wataru. As a fan, that makes me think they might bring the main casts form the previous series, making Decade like a reunion series, like the annual Super Sentai versus where new casts meet the old casts. Alas, that's not the case. So far, all the other Rider's world are alternate universe, and no cameos at all. Even Kiva's world episodes didn't have Seto Koji in it. Forget about Mizushima Hiro returning as Kabuto then, he's probably too busy with his new marriage and movie. Also, no Takeru Sato in the Super Den-O and Decade movie either. No Kento Handa in the Faiz world either (even though he appeared in Go-Onger).
2. Kamen Rider Decade started with a bang, the Rider War. All the special effects and CG you can think of is in the 1st episode. Fast forward, now they have to use a freakin in-animated toy for Kivala. It was so obvious that it's just a toy with a string. Very embarrassing for a show that have been using CGs heavily, especially for the Final From Ride transformations.
3. Decade can use a Final Form Ride card, and "transform" any of the riders into a weapon or some sort. WTF? It's just weird. This is not Transformers. This is obviously a ploy to sell toys.
The belt is very neat though, but you have to buy the other toys to get more cards.
Good thing that Shinkenger seems to be a better show.