Kamen riders... assemble!
 

I'd imagine that the kamen riders create a team of avengers. When I mean the riders, I mean the primary ones.

I'd imagine....

Leader - Fourze
Double/W
OOO
Wizard
Gaim
&
Drive (newcomer)

If only they made a movie out of that.

Decade?
Then it means he's going to be killing the other characters except not really as it's part of a big plan to trick the villain that everyone but the audience seems to be in on because it always seems to happen when Decade gets a lead role.
Make the leader Fourze. His energy and optimism will help convince the others to actually join together.

Alright then. Decade is OUT!

Does it have to be only Main Riders? Because I can see better team dynamics being made with a wider pool of characters to choose from like the Secondary & Extra Riders.

Well, I mean. Fourze could be the Captain America equivalent. Decade could be Nick Fury.

Needs a female.

Black Widow y'know?

Nadeshiko
Marika
Femme
???

Femme and Marika are kinda shady...


My team:

Ichigo-Captain America

Kabuto-Iron Man

Gills-Hulk

Femme or Marika-Widow

?-Thor

?-Hawkeye

Kamen Rider 1 - The veteran
Kamen Rider Kabuto - The speedster
Kamen Rider Gaim - Godlike dude
Kamen Rider Decade - The wild card
Kamen Rider J - The jolly green giant
Kamen Rider Wizard - The arcane specialist

I though about what the Rider equivalents of the Avengers would be a while ago, and came up with this:

Captain America - Ichigo
Iron Man - Fourze
Hulk - Shin
Thor - Kiva maybe?
Fury, Hawkeye, and Black Widow - Glaive, Lance, and L'Arc

TaToBa could be Hawkeye. BUDUM-TSSS!

Who can be leader can be Gaim, W or OOO.

Ok for mine:

Leader: Gaim
W (2nd in Command)
Fourze (Techological)
OOO (Shapeshifter)
Kabuto/Den-O (Timechangers)
Femme (Token Female)

I actually had a team for this exact premise for a while:

Captain America/Ichigo
Iron-Man/Kabuto
The Hulk/Gills, I suppose?
Thor/Bravo
Hawkeye/Chalice
Black Widow/Femme
Nick Fury/Decade

Bravo as Thor?... What? Care to explain?

I think Gaim makes a bit more sense in light of the fact that, well, he's now fruit space Jesus from another world.

I'm adding the Avengers 2 characters because I like them and can lol.

Captain America-Baron (In the thirties of Gaim he was a great leader)/Zangetsu (He was the leader of Yggdrasil and if everyone didn't betray him can be a good leader, also has the shield).
Nick Fury-Garren (has a gun, runs an Organization with an anagram, and lost an eye in a sense lol.)
Hulk-Another Agito (He's a Doctor and He went uncontrollable at times, had depression and rage issues like the Hulk and being an Agito has a lots of strength.)/ZX (Was part of an experiment, and definitely has a lot of power and Rage issues after what happened to him especially what happens in the Spirits Manga.)
Black Widow-Satonaka/Kiriko (Black Widow doesn't have powers and these two women are extremely well-trained.)
Hawkeye-Riderman (Was evil in the beginning then went good, kind of similar to Hawkeye's comic origin and similar to the movie being possessed. Also his different arms work like different arrows.)
Iron Man-Kabuto (Smart, Cocky, and thinks he's God, pretty sure that describes both Tendou and Tony.)/W (Both Shotaro and Philip together they combine for both the Cocky side of Tony and the Smart side of Tony. So definitely could work.)
Thor-Decade (They come from different worlds both have to deal with 9 Worlds/Realms, insanely powerful and both can be arrogant and helpful.)
Quicksilver-For just the speed Drive/Accel. For the Speed and close to the character and speed I'll go Kick Hopper/Faiz.
Scarlet Witch-Wizard (because of Magic)/Gaim (because of his God-like powers now and kind of similar personalities).
Vision-OOO (Not an android-like being but definitely has the similarities with the multitude of powers.)

To me, I've always seen Thor as the bruiser of the group, who loves battle and loves a good fight, which reminds me of Bravo quite a bit. He can also be a loyal and reliable companion when he needs to be.

Decade would be the only one to bring them together. Decade it totally nick fury.