Though ExKaiser isn’t exactly like Brave Police, I’d say its pretty close compared to the rest of the Yuusha series (That I’ve seen. I’ve only seen Da Garn, one episode of Fighbird, and a bit of GaoGaiGar.)

There’s always moments where Kouta is like ‘Oh ExKaiser would like this. I wish ExKaiser was here, etc. etc.’ which really shows they have a relationship beyond saving the planet??
Plus Kouta usually ends up talking to ExKaiser in his garage occasionally
Though, as far as I’ve seen Kouta doesn’t really talk to the other Kaisers as much, and rarely communicates to them I guess??

In Da Garn, Seiji talks to Da Garn, but he doesn’t really treat him on a ‘personal level’ I guess
Da Garn also doesn’t show too much emotion either, unlike ExKaiser who frequently is worried about putting Kouta in harmful situations and objects when Kouta suggests he helps in dangerous situations

It’s more focused on Robobonding than most of the other series I think, as well as the ‘save the planet’ sense too. Brave Police still remains one of my favorites, but ExKaiser is a really close second.