So maybe something like pills or gashapon capsules, cure capsules for or hero and infection capsules for the bad guys. Problem with that is that it could be too close to drug abuse for a kid's show

It's also very easy to repurpose something designed for war, like a helicopter, as something for peace or relief. And vice-versa.

Look at how many variations there are of the UH-1, for example.

Do you expect Ex-Aid Rider to have a different personality from Takeru?

It's NOT Super Sentai where Red Ranger always have a same personality of a loud-mouthed, hot-headed buffoon

Kamen Rider have their Main Rider a different personality unlike Super Sentai but they always give a same "Anti-Hero try to be badass" personality to secondary rider

Dopant Memories were basically drugs in W, so I don't think your idea would be out of the question.

The Second Rider typically has an attitude/personality and occasionally motivations that conflict with the Lead Rider. The Second Rider is the foil. Typically the Lead Rider is a fairly energetic or upbeat person, and so the Second, naturally, is more melancholic. It makes for a good if predictable dynamic (recent subversion in Drive with the roles reversed- Shinnosuke being fairly serious and Gou being the upbeat one) that keeps us from (usually) having an entire cast of shrieking, yammering idiots like tends to happen in Super Sentai.

Point being that tropes and archetypes exist for a reason- what's important isn't THAT they're used, it's HOW they're used.

Anyway yes, I hope the Lead is different from Takeru. He's... Haruto without everything that made Haruto endearing.

And I didn't even find Haruto that interesting.

True, but with them being pills or capsules the relation would be more apparent, but it depends if the humans turning into Kaijin use the of their on free will like W or it's more like OOO where they are forced to take it

That's why Beast was energetic, lively, and worked to further the plot.

Or it might have been mentioned earlier in this thread.

Sometime...I am really want Secondary Rider is pure evil (never become good guy) and Third Rider is Hero Rider......

I wonder if we will get a doctor for Ex-Aid's civ identity.
That would be cool.
Or male nurse could work as well.
And then we get Date-san from OOO as a guest in a v cinema film team-up.