The only idea I really have for that is to have the belt have a face, and the collectible gimmick would be tiny masks that you put on the belt face, and then the actual mask and related accessories materialize on the Rider.

(it is at this point that i admit to large bias from bionicle and mask collecting in this idea)

It would definitely make for the single most logical iteration of legend rider gimmick items in existence...

How about a Psychic powers season? Bad guys want to force everyone into a hive mind state, while the Rider fights for individualism. There's a hunt for items that late either the kaijin or the rider see into the future as well as expand one's mental powers.

Victims of the week can be influential people that the kaijin want to eliminate/corrupt, as they're at a part in their life where they decide what their future will be.

The rider could have had an original idea/dream stolen from them by a rival, who now works with the kaijin with the agreement that parts of his personality will be dominant in influencing the hive-mind once constructed.

Rider Key Items & gadgets
 

Seeing how the riders use key items now, well....
Cards: Ryuki, Blade & Decade

Hibiki: Discs

Whistles: Kiva

USB Drives: Double
- Memory Gadgets - based on electronics

Medals: OOO
- Candroids - based on soda cans

Fourze: Switches
- Foodroids - based on fast foods

Wizard: Rings
- PlaMonsters - based on plastic models turning into mythological creatures

Gaim: Locks

Toy Vehicles: Drive

Now...

Eyes: Ghost
- Ghost Gadgets - based on old antique items

Next series they should do one of these....

- keys (like Ryukendo & Gokaiger)
- batteries (like Kyoryuger)
- spinning tops (like Beyblades) - I can imagine the blade piece of the top to look like shurikens.
- amulets
- fossils

Are you suggesting that a flip phone ISN'T an antique at this point? :lol

Hibiki would like a word with you... OH, you mean to transform? I guess. Still sort of seems like a do-over.

How about teeth as a collectible item? Rider can have them arranged on their belt like an old hunter might, and he gains special ones for defeating certain kaijin.

Not in Japan. Those are still way in use.

Does it define for being ghosty/ghostly?

They sure spook me.

How would u all bring out a....

- Music rider series: .....

- Sports rider series: .....

and a...
- Rescue rider series:....

Hibiki, the way it was meant to be. ;_;